摘要:

Summary.The scores obtained by the three colours of insects “n,”“l” and “i” on background “n” are 163, 271 and 376 respectively, and show that insects differing greatly from the colour of the background are destroyed, while those agreeing with it are preserved. Insects coloured “l” are only partial misfits and occupy an intermediate condition. These conclusions are confirmed by the experiments on background “i,” where the order of destruction is reversed. The scores of 270, 284, 278 and 274 obtained by insects coloured “1” on backgrounds “a” to “g” respectively suggest that these differences have no significance, but are fluctuations about a mean value (probably 270). The scores obtained by insects coloured “n,” 362, 300, 282 and 270 for back‐grounds “g” to “a” respectively, show that on passing to the lighter backgrounds the scores approximate more and more to those of insects coloured “1.” The insects coloured “i” obtained scores of 174, 232, 244 and 270 for backgrounds “g” to “a,” and show a similar tendency. As the difference between the colour of the background and the insects increases, any variation in the colour of the latter is rendered more and more inconspicuous, and in consequence the fish find more difficulty in distinguishing between the three types of prey. One advantage of the Ostwald Colour Chart is that there is a constant apparent difference between two adjacent standards, and, therefore, the predators must experience the same difficulties in distinuishing between insects coloured “1” and “i” on background “a” as between insects coloured “n” and “1” on background “c.” This means that the scores of 270 obtained by insects coloured “1” and “i” on background “a” are a measure of the extent to which the predator is able to distinguish between the two types of prey differing from the background by four and five standards, and these can therefore be added to the scores of 282 and 284 obtained by insects coloured “n” and “1” on background “c.” Combining these two sets of figures, it will be seen that the scores of 552 and 554 were obtained by insects differing in colour from he background by five and four standards respectively. Experiments performed with greater accuracy might show that predators can distinguish between these two types of prey. Even if the results obtained from the original set of experiments on background “a” are combined with the above figures, the scores are increased to 7718 and 784 respectively, still failing to give any evidence of selection. Another advantage of the constant apparent difference between any two adjacent standards is that it is possible to compare the results of any one set with those of the next, and so combine all the sets and deduce the results which might be obtained were seven sets of insects (coloured. “a” to “n”) used on backgrounds (‘i “and’(n.” The calculations are very simple, as th

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08478.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY

摘要:

Summary.1. The darkening of the puparium inDrosophilaprobably involves a tanning reaction similar to that described forCalliphora.It is reduced inebony, black,andstraw‐3,and changed in nature, so as to give a yellower tint, inyellowandyellow‐2.It is somewhat increased inspeck,particularly in the region of the anus, where there may be a sharply marked dark band.2. The pigmentation of the wild‐type adult is due to two processes, a browning which is probably a tanning, and a blackening which is probably a deposition of melanin. The browning is more apparent in the earliest stages of pigmentation, and first affects the chsetse, the darkening of the cuticle becoming stronger at a later stage, chiefly after emergence.3. Inyellowthe browning is changed into a yellowing, and the blackening much reduced. The change in the character of the tanning occurs earlier inyellowthan inyellow‐2,so that in the latter the bristles are pigmented normally.4.Straw‐3reduces both phases of pigmentation, whileebony,and to a less extentspeck,increases both phases.Blackintensifies the blackening more strongly than the browning.5. In compounds ofblackandebonywithstraw,the early stages of pigmentation (of chætæ) proceed as instraw,while the later ones (of cuticle) proceed as inblackorebony.It is argued that this indicates thatblackandebonyact earlier in the reaction sequence than doesstraw.6. It is clear thatebonyaffects not only the quantities of pigments formed, but also the time at which they make their appearance, since it reduces the tanning of the puparium and increases that of the adult. It is suggested that this may provide an explanation of the behaviour ofebonyas a

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08479.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY

摘要:

Summary.1. In flies homozygous forthickthere is a partial failure of the contraction of the leg from the highly inflated condition characteristic of the beginning of the true prepupal period; the same is true, to a lesser degree, of the wings.2. This is preceded, and probably caused by, an over‐contraction of the longitudinal larval muscles at the time of puparium formation, which is such as to give rise to an increased fluid pressure inside the body of the animal.3. Inhumpyflies there is an over‐contraction of the epidermis of the wings and thorax, which is responsible for the shortening of the wings and the formation of grooves and “vortices” on the thorax.4. At the time of puparium formation, the larval muscles ofhumpycontract irregularly, and a similar irregular muscular contraction plays a part in producing the deformations during the beginning of the true pupal period‐ The abnormal larval contractions sometimes cause modification of the normal internal anatomy, which in their turn result in irregular eversion of the legs, leading to abnormalities in their later contraction during the pupal period.5. It is pointed out that such a mechanism reduces the difficulty of understanding the apparently dissimilar effects of the differentdumpyallelomorphs, some of which produce thehumpytype of wing while others produce thehumpytype of thorax.6. The relevance of the data for the general theory of development is briefly

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08480.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY

摘要:

Summary.1. Translocations of different regions of the organizer were carried out in young gastrulae ofDiacoglossus pictus.In one series of experiments the presumptive anterior mesoderm was exchanged with presumptive posterior mesoderm; in another set the anterior‐posterior axis of the presumptive axial mesoderm was reversed.2. The translocated pieces retained their original potentialities for gastrula‐tion movements, both in magnitude and direction.3. The gastrulation movements of the host and of the graft were such that only very incomplete mingling of anterior and posterior regions was brought about; and, perhaps for this reason, little evidence was seen of any inductive interactions between different regions.4. There was very complete regulation of the host to form a complete embryo within which the graft lay as a more or less independent mass of tis

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08481.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY

摘要:

Summary.1. The structure of the compound eye ofDrosophila melanogasteris described in detail.2. The development of the normal eye is traced from the late larval to the adult stage. The chief features of the development are as follows:–(i.) The optic disc differentiates into three layers. This process is affected byGlued.(ii.) The middle layer of the three. penetrates the outer layer regularly. This process is affected bysplitandGlued.(iii.) The middle layer cells next divide to form the cells of the pseudocone. Thisjprocess is affected bysplitandGlued.(iv.) The cone cells further divide to form the retinulse. This process is affected byGlued.(v.) The retinulse are excluded from the cone‐cup formed by the outer layer of the disc.(vi.) The cone cells and retinulse develop and secrete the pseudocone and rhabdome.Boughcauses this process to be irregular, and the amount of secretion is influenced bysplitandGlued.3. The structure and development of the facet‐mutantsrough, split,andGluedare analysed in detail, and a table is given comparing their structure and development with the wild‐type eye.4. The nature and origin of fused, flat, and erupted facets is described. The fused facets ofroughare different in origin from those ofsplitandGlued.Two varieties of flat facets are found, one of which is present inrougharid the other inGlued,whilst both are found insplit.The “cupless” flat facets ofroughandsplitthough similar in nature are different in origin.5. Two rules governing the relationship between the retinulse and cone cells, and the retinulse and the shape of the facets, are stated. The wild type andsplitadhere to both rules, whilstroughadheres to one rule up to th? end of the second pupal day andGlveddoes not adhere to either.6. The structure of the periopticon in the wild and mutant types is described, and the origin of the periopticon in the optic stalk is confirmed by

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08482.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY

摘要:

Summary.Evidence of attacks upon butterflies by birds is provided by the imprint of the beak upon the wings. Comparison is made between the frequency of such beak‐marks in butterflies which have the characters of relatively distasteful species and in others not so characterized. Over 14,000 specimens belonging to three different groups were examined for the purpose, and the difference in frequency of beak‐marks was found to be immensely significant statistically. The marks are ten times more frequent in the more “distasteful” species. In addition, 567 models and 341 mimics, forming several African mimicry associations, showed that there is a significant difference between them in frequency of beak‐marks in favour of the models. These facts are interpreted as evidence of the greater destruction of species not furnished with aposematic characters, which, when attacked, do not escape like the tougher, more distastefu

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08483.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY

摘要:

Summary.A survey of the cleavage‐process in the later blastodiscs comprised in Group I shows that the division of the blastomeres follows no very regular plan and that there is often a considerable time‐lag between nuclear and cytoplasmic division.The central blastomeres, somewhat more flattened and more ovoidal in form than in the 31‐ and 32‐celled stages may divide before or after they have become delimited from the yolk‐bed. In the former case division usually appears to be effected in a plane oblique to the surface and is slightly unequal. It results in the formation of a larger superficial cell and a smaller deep, which lies not directly below its sister‐cell but obliquely thereto. Both remain for a time in continuity with each other and with the yolk‐bed. In the latter case, when the blastomere divides after delimitation, it may do so in the vertical plane to furnish two superficial cells or in the horizontal plane to form a superficial and a deep cell.The deep cells separate sooner or later from their superficial sister‐cells and then become delimited from the yolk‐bed, first in the central region of the disc. It seems probable that some few of them may divide prior to their delimitation, the deeper of the two daughter‐cells forming a sub‐disc cell, which is later incorporated in the disc. The distinction between marginal and central cells (so obvious in the 31‐ and 32‐celled blastodiscs) is soon lost (in LC. 4), the marginal cells being used up in the production, on the one hand, of peripheral disc‐cells, and, on the other, of peculiar cells possessed of migratory properties and the capacity of enclosing yolk‐spheres which lie at first just outside the periphery of the disc, but some of them soon wander outwards below the egg‐membrane, away from the latter, whilst others migrate inwards below the yolk‐membrane, to underlie the periphery of the disc. These cells, or vitellocytes as we have termed them, are already present in the 41‐celled disc (LC. 1). In succeeding stages they increase in number by division and are destined to fuse together to form a continuous zone of nucleated cytoplasm which encircles the disc and extends inwards for a very short distance below its periphery. This zone constitutes the germ‐wall, the presence of which conditions the growth in surface‐extent of the blastodisc and its concomitant transformation into a thin blastoderm, capable under its continued influence of growing round to enclose the yolk.In the earlier stages under review, the superficial cells increase in number much more rapidly than the deep; in LC. 4, for example, the former number 44 and the latter 12, but in the interval between LC. 4 and LC. 5 the deep cells, as well as the superficial, have undergone division so actively that the disc in its central region has attained a thickness of about four cells, thinning out peripherally to a thickness of two cells and to one at the margin. Except over a very restricted area below the central, region, the underside of the disc is still very irregular and lacks a definite contour, many of the deep cells being still open to the yolk.The delimitation of the deep cells from the yolk‐bed results from a process of rounding off or constriction affecting the region of continuity of the cytoplasm of the cell‐body with the. cytoplasmic reticulum of the yolk‐bed. As soon as a number of contiguous deep cells have become delimited, a thin limiting membrane (the yolk‐membrane) is differentiated on the surface of the yolk‐bed. It first appears in LC. 5 below a restricted area of the central region of the disc, and in LC. 6 it has also been established in places below the periphery of the disc. In LC. 7 it has been completed below the greater part of the disc. In this way the disc, as a whole, becomes delimited from the yolk‐bed, though more or fewer of its peripheral cells remain open to the yolk. It is circular and biconvex in form, measures just over 0‐5 mm. in diameter x 0‐08 mm. in m

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08484.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY

摘要:

Summary.1. The bridled form of the Common Guillemot(Uria aalge)is a single factor mutant, which is present in varying proportions over the North Atlantic colonies of that species.2.‐ Counts were taken, with the help of the British Trust for Ornithology, at the breeding cliffs during the summers of 1938 and 1939, and the proportions of bridled to normal birds ascertained.3. The full results show that the percentage of bridled birds increases from south to north and, in a less degree, from east to west. This cline in dimorph‐ratio is not even: in the British Isles the population shows sudden increases in the bridled percentage at two zones, the Mull of Kintyre and the channel between Pair Isle and Shetland. In Iceland the cline is reversed in sign and the percentage of bridled birds decreases again from the south to the north.4. This stage of dimorphism may be due to the unimpeded spread of an advantageous mutation, or it may be reaching a balanced condition owing to counter selection at various levels by environmental factors. This balance might or might not have been reached; a repetition of the inquiry after ten years should settle this question. Coincidence of the cline with an increase in humidity northwards and westwards is noted.5. Statistical analysis of ledge counts shows that there is no heterogeneity within the separate colonies, with the exception of Mingulay, where a special factor seems to be in operation. This suggests the absence of any marked degree of assortment. Fisher's hierarchicalx2test demonstrates the step‐like nature of the cline over the region from the Faeroes to the Hebrides. In particular, there is local heterogeneity but no general trend in dimorph‐ratio over the area stretching from Fair Isle to M

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08485.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY

摘要:

Summary.1. The display ofRheinardiais here illustrated for the first time. The bird forming the subject of this communication was bred in the Society's Gardens at Regent's Park. It is a typical lateral display in which the vertically spread tail plays the major part, while drooped wings and erected crest also contribute.2. A preparatory stage is figured in which the crest is erected and the tail partly spread. The bird may spend considerable periods in this attitude.3.Rheinardiadiverges in its type of display from the rest of theArgusianinse,in which display is frontal.4.Rheinardiaflies better thanArgusianus,in which the wings have become converted into display organs, relatively useless for flight.

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08486.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY

摘要:

Summary.1. The ten recognized subspecies ofTamandua tetradactyla(Linn.) are defined mainly by skull proportions. The differences between these subspecies have been analysed with the aid of statistical methods based on the allometry formula, in order to discover how far neglect of the fact that many proportions change with size has led to false conclusions.2. In order to provide a background for the statistical analysis, all available information on the characteristics and distribution of each race is first summarized, and controversial points discussed. The main points are as follows:–(a) Tetradactylaandlongicaudataare not clearly defined. The latter seems to be distinct only in fur pattern, lacking the usual striping.(b) Instabilisandquichuashow parallel characteristics with races of other mammals from the same localities, suggesting their peculiarities are due to ecological factors.(c) Onlylongicaudata, quichua,and possiblytetradactylaare distinguishable by their coat characters.(d)Tail‐lengths appear to fall into two size groups,chapadensisandinstabilishaving shorter tails than the rest. Tail‐length ininstabilisis uncorrelated with head and body‐length, suggesting that its short tail is an independent character, not due to its small body‐size.3. Allen's classification ofinstabilis, chapadensis, mexicana,andchiriquensisinto two groups, based on relative nasal length, is found to be erroneous.Instabilisappears to be a small edition ofmexicanaandchiriquensisin the skull characters studied, whilechapadensisdiffers from the others in having a greater extension of the frontals at the expense of the nasals.4. Study of other skull characters suggests that the status of most of the races is dubious. Skulls from nearly all regions show marked variability in proportions, and there is no clear tendency for proportions to change with geographical position.5. Comparison of ranges and means suggests that onlychapadensisandmexicanahave any claim to be considered distinct subspecies on the basis of skull proportions.Chiriquensis, punensis, tambensis,and specimens from the Middle Amazons cannot with certainty be distinguished from the British Guiana form,tetradactyla. Sellatais probably identical withmexicana.The latter's sole peculiarity seems to be its relatively narrow rostrum.6. It is clear that proportional differences between two groups of animals cannot be accepted as evidence of taxonomic distinctness, when size differences occur, without further analysis. The tests described have been found satisfactory for the purpose of analysing proportional differences.7. The danger is emphasized of basing taxonomic classifications on small samples. Before subspecies are defined it is necessary to collect large samples from different regions and to study the fluctuational variability. Among mammals this is usually large for all quantitative characters.8. Adequate data for the study of rare animals such asTamanduawill only accumulate if museum taxonomists regularly publish comprehensive measurements of the specimens in their care. It is important to make available the individual measurements, since otherwise statistical analysis is severely restricted.9. All original measurements will be deposited in the library of the British Museum (Natural History

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1942.tb08487.x

出版商:Blackwell Publishing Ltd    

年代:1942

数据来源: WILEY