摘要:

Summary.1The material consisted of 957 males, 1,529 females, and 1 inter‐sex of wild rabbits obtained in Caernarvonshire between February 1941 and June 1942, inclusive.2No sexual dimorphism in cleaned body weight was observed. The 1150–1199‐gm. weight group was that of greatest frequency in both sexes, and very few animals were obtained exceeding 1500 gm. in weight. Body weight does not provide a good criterion for distinguishing adults from young in either sex. The average weight of young at birth probably is between 40 and 45 gms.3The testes of adults reach a maximum size in April. They then decline in weight by over 60 per cent., reaching a minimum in July. The testes begin to increase in weight again in August. The drop in weight is accompanied by a decline in spermatogenesis, and it begins during the height of the breeding season, one month before the decline in the pregnancy rate.4Copulation occurs at least twice as frequently with non‐pregnant females which are not in œstrus as with those that are. Copulation also occurs frequently with pregnant females at all stages, but especially during the first four days of gestation. These copulations with females that are not in heat are most frequent during November, December and January, that is, during the quarter preceding the breeding season.5The breeding season in Caernarvonshire is sharply defined; it begins in January and ends in June. More than 50 per cent, of females were pregnant for 17 weeks in 1941 and for 15 weeks in 1942.The 1942 breeding season was slightly earlier than that in 1941.6Practically all females become pregnant again at eachpost‐partumœstrus during the height of the breeding season. An exception is provided by the period of severe frost in February and March 1942, during which many animals failed to become pregnant at thepost‐partumœstrus. During March April and May over 80 per cent, of animals suckling are pregnant.7Young females born early in the breeding season may breed before the end of it, or in the late summer or autumn.8True pseudopregnancy is very rare in the wild animals.9It was concluded that the time of the onset of the breeding season is determined by the females, but that its close is determined by the males.10The wild rabbit differs from the tame rabbit chiefly in (a) the sharp delimitation of the breeding season, (b) the intensity of breeding during the season, (c) the maintenance of pregnancy during lactation normally, and (d) the extreme rarity of true pseudopregnancy.11The pre‐natal mortality during 1941 has been dealt with in a preliminary paper (Brambell, 1942). The conclusions arrived at are confirmed and extended. The proportion of litters showing loss was slightly higher in 1942 than in 1941, but this discrepancy is accounted for by (a) the difference in litter size in the two samples, and (b) experimental error.12It is estimated that 60 per cent, of litters conceived are lost owing to the death and reabsorption of all the embryos.13The proportion of litters showing loss is related directly to the initial size of litter. It is not related to (a) the cleaned body weight of the mother, (b) whether the litter is the first of the season or a subsequent one, (c) whether the mother is or is not suckling.14It is shown that animals which have borne a living litter are as likely to lose the next, and no more likely, than those that have lost a litter already.15The majority of the embryos die on or about the twelfth day.16The possible causes of this extraordinary mortality are discussed.17The loss of ova in litters that survive to birth is between 9 and 10 per cent.18The number of ova ovulated at œstrus, as shown by the number of corpora lutea in the ovaries, varied from one to nine, five being the most frequent. The mean number was 5·36 for the whole sample. There was a significant difference in the mean numbers for 1941 and 1942 respectively, the former being 4·89 and the latter 5·64. The mean number of ova ovulated is related directly to body weight. It is shown that for a given body weight the mean number of ova ovulated was greater in 1942 than in 1941, but the increase in the mean number of ova ovulated for a given increase in body weight was similar in the two seasons.19It is calculated that the most productive initial litter sizes are five and six, the inflection in the curve of number of embryos expected to survive according to initial litter size being at 5·7.20A few instances in which the number of embryos exceeded the number of corpora lutea are recorded. These must have been due either to poly‐ovular follicles or poly‐embryony. Six instances of transperitoneal migration of ova are recorded, five being from right to left and one from left to right.21It is estimated that the mean number of young born to each adult female is between 10·35 and 11·70 per annum.22The post‐natal sex‐ratio of the whole sample was 50·49 ±0·76 per cent. males. The fœtal sex‐ratio was 48·65 ± 1·045 per cent, males, which does not differ significantly from the post‐natal ratio. The frequency of sex combinations in littersin uteroshows an excess of observed over expected values in the central classes which may be significant.23One definite intersex and some other abnormalities were

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00210.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

摘要:

Summary.1The development of egg‐fragments, isolated blastomeres, and fused eggs of the goldfish (Carassius) is described in the present paper.2Fragments derived from eggs about four to forty‐three minutes after fertilization give rise to (i.) perfect embryos of half size, (ii.) abnormal embryos of all degrees, and (iii.) rounded or oval vesicles without any histogenesis. The nearer the time of operation to the time of fertilization, the more perfect the embryos obtained.3Blastomeres were separated following the first or second cleavage plane in the 2‐, 4‐, and 8‐cell stages. The development of these isolated portions varies from the formation of two typical embryos of half size to two vesicles without any histological differentiation. No constant relation between the cleavage planes along which the eggs were separated and the subsequent development of the blastomeres was observed.4Two eggs were fused in the stage of two to thirty‐two cells. The double egg may produce a single perfect embryo of double size or twin embryos either normal or abnormal in structure.5The segmentation of the egg‐fragments is the same as that of the whole egg, while that of the isolated blastomeres is partial, as though still a part of the whole. The divisions are not always equal. A normal embryo, however, may develop from a fragment of unequal division; conversely, a fragment of typical division may give rise to an abnormal embryo.6The abnormal embryos derived from the egg‐fragments and isolated blastomeres are quite variable in form and structure. In some cases the head is well formed while the trunk is abnormal; in other cases the trunk is typical but the head is missing; in still other cases only a tail‐like body is formed.7The nerve‐cord is not always associated with the notochord; a well‐elongated neural tube may be formed without a notochord. No evidence is found that the latter can change the differentiation of epithelial cells with which it is in contact.8In some vesicles developed from the egg‐fragments and isolated blastomeres abortive independent differentiation of somite and nervous tissue is found. A feeble determination of “organ‐forming substances” occurs, therefore, in the very early stages of development.9It is supposed that in the egg of the goldfish there exists some centre comparable to the amphibian grey crescent, from which the organizer region later arises. The normal process of development is based in part on the action of the organizing centre and in part on the self

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00211.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00212.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

摘要:

Summary.1Collections of three species of Corixids were made at regular intervals from a small pond at Wilpshire, near Blackburn, Lancashire.2After fifty Minnows had been introduced the proportions of Corixids adapted to the habitat increased.3Various possible explanations are considered, and it seems most probable that the Minnows destroyed those insects which did not harmonize with the background.4There is a lower intensity of selection under natural conditions than that observed in the laboratory.5The influence of selection and isolation in the spread and preservation of various types of characters is also discussed.

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00213.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

摘要:

Summary.Beyond the somewhat obvious deduction that the present subdivision of the genus is ill‐founded, it must be admitted that no clear conclusion can be drawn from the facts adduced. All that is claimed is that they justify an appeal to those to whom specimens are available of species not adequately described to re‐examine them and provide the information upon which a revision of the genus may be foun

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00214.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

摘要:

Summary.1The development of the middle ear is described inEremitalpa, ElephantulusandEriculus.The structure inEremitalpais fundamentally more primitive and quite distinct from that seen inEriculus.2The interossicular joints are in some cases clearly incapable of movement.3Evidence is brought forward for the view that the manubrium mallei and the element of Spence represent the insertion and horizontal portions respectively of the reptilian extrastapes,

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00215.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

摘要:

Summary.1The use of polarized light is recommended for working out the anatomy of the muscles.2A neuropodium consists of a single dorsi‐ventral row of sigmoid chætæ, each in its own follicle. There is a continual dorsalwards procession of chætæ and follicles along it. New ones are formed at the ventral end, and old ones break down into a green, granular mass at the dorsal. The green matter collects for a time and is then cast out.3The neuropodium is provided with protractor and retractor muscles.4A notopodium is more complicated than a neuropodium, but built on the same fundamental plan. It can be conceived as a neuropodium in which the plate formed by the chætæ and follicles has (i.) changed its shape, (ii.) split into two parallel plates in close apposition, (iii.) rolled up into a scroll, and (iv.) acquired an invaginable base, by thinning and protrusion of the surrounding body wall. Chætal destruction and replacement proceeds as in the case of the neuropodium.5The intricate musculature of the notopodium is fully described in the text; it includes muscles corresponding to those of the neuropodium, and others which appear to be derived from new components.6Apart from the movements of the notopodia and neuropodia, the more anterior chætigerous annuli can perform distinctive “flanging” movements of their own.7Besides bearing the appendages, the chætigerous annuli are distinguished by important peculiarities of their general structure. These are most clearly seen in the first three segments, where each chætigerous annulus has (i.) an extension of the body cavity, the “parapodial canal,” looping round inside it; (ii.) a special musculature associated with the parapodial canal; (iii.) an externally visible “hinge‐line,” roughly bisecting the annulus; and (iv.) another special musculature associated with the hinge‐line.8The generally held view that the parapodial base has disappeared inArenicola, leaving the notopodium and neuropodium to arise separately from the body wall, is apparently not true of the first three chætigerous annuli. The whole of any one of these annuli can be regarded as derived from a pair of parapodial bases, which have expanded dorsally and ventrally to form a girdle encircling the worm.9The fourth to nineteenth chætigerous annuli are described as each consisting of (i.) a “parapodial component,” containing special structures like those seen in the first three, and (ii.) a “body‐wall component,” from which these peculiarities are absent. As one passes backwards, the body‐wall component comes to occupy more and more of the annulus, at the expense of the parapodial component.10The gills and nephridiopore

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00216.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

摘要:

Summary.1The heart and vascular arches ofIchthyophis, Ureotyphlus, Gegenophis, Scolecomorphus, Boulengerula, DermophisandHerpelehave been described and compared with those ofHypogeophis, SiphonopsandChthonerpeton.In the first six genera, there are two systemico‐carotid arches which give rise cranially to the right and left systemics. The two systemic arches unite to form the dorsal aorta. In all six genera there are paired pulmonary arteries, except inGegenophis, where there is only one which is on the right side. InHerpelethe truncus gives off a right systemic and a large carotid arch, and from the cranial end of the latter there is a branch (lateral dorsal aorta) connecting it with the right systemic arch; a small pulmonary is given off before this union. The conus has a double (Ichthyophis, Dermophis, Herpele) or a single (Ureotyphlus, Gegenophis, Boulengerula, Scolecomorphus) row of valves. The truncus usually shows a septal‐fold described as the “spiral‐fold” inHypogeophisandIchthyophis, but a spiral valve is absent in the conus.2The musculature of the heart is continuous throughout, there being no nodal tissue in the sinus, or at the junction of sinus and atria, atria and ventricle or ventricle and conus. In this the Apoda resembleSalamandra.However, the basket‐work nature of the muscle observed in the sinus and atria ofSalamandrais not seen in Apoda; the circular musculature at the S‐A opening is also not developed in Apoda, the S‐A valve being formed by the walls of atrium and sinus in that region.3There is a large sinus ganglion only (corresponding to Remak's ganglion of the frog) and those corresponding to the atrio‐ventricular ganglion of the Salamander (or Bidder's ganglion of the frog) and the bulbus ganglion of Salamandra are not found in Apoda. A few scattered nerve cells are seen in the fenestrated inter‐auricular septum as in the Salamander; thus both in Apoda and Salamandra, a ganglion corresponding to Ludwig's is absent.4The inter‐auricular septum is fenestrated and is connected caudally with the membranous bicuspid valves as in Urodela. The musculature of the septum is continuous with that of the atrium.5The A‐V ring and A‐V funnel are comparable, point for point, with those of the Salamander; the A‐V ring is sphincter‐like and the muscle fibres of the funnel are connected anteriorly with those of the ventricle and posteriorly with the papillary muscle fibres.6A scheme of the circulation of the blood is described. InIchthyophis, UreotyphlusandBoulengerula(probablySiphonopsalso) the cavity is divided into lateral chambers by a dorsoventral septum in the truncus and into dorsal and ventral chambers by a lateral septum inDermophis, since the left lateral, or dorsal, chamber, as the case may be, divides cranially into left systemico‐carotid and pulmonary arches, these will convey venous blood. The right systemico‐carotid and pulmonary arches, arising from right lateral or ventral portion of the truncus, will contain arterial blood. This finding is opposed to that of Acolat (1939), who said that inIchthyophisthe slight twist of the “spiral‐fold” in the truncus made the venous blood flow into the pulmonary arches which arise dorsally. InGegenophisthe pulmonary artery arises as a dorsal trunk on the left, while the two systemico‐carotids are given off from a larger ventral chamber of the truncus; the pulmonary artery takes venous blood to the lungs. InHerpele, where the truncus is divided into right and left lateral portions, the systemic and pulmonary arteries arising from the right side of the truncus will carry arterial blood, while the carotids contain venous blood; there is, however, a connecting vessel between the right carotid and the systemic arch.7The study of the developmental stages ofIchthyophisshows that in both embryos and larvæ three vascular arches only, the third, fourth and fifth entering the external gills as afferent branchials are present; Sarasins described these as third, fourth and sixth visceral arches. The third disappears, the fourth forms the systemico‐carotid and the fifth the pulmonary arte

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00217.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00218.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

摘要:

Summary.The distinctions between the generaScleronemaEigenmann andTrichomycterusValenciennes can hardly be considered as of generic importance; however, the nameScleronemais retained here till further material is investigated.Three species ofScleronemaare revised,Scleronema operculatumEigenmann,Scleronema minutum(Boulenger). andSleronema angustirostrisThe distinctions between the two species are apparently due to the difference in size of specimens described, but as the types ofScleronema operculatumcould not be examined no conclusion on the existence of this species is made.The generic name ofHatcheriaEigenmann is considered as synonymous withTrichomycterusValenciennes; the name ofTrichomycterus areolatusValenciennes synonymous withTrichomycterus maculatusValenciennes; the name ofTrichomycterus burmeisteriBerg synonymous withTrichomycterus macraeGirard.The change of the name ofTrichomycterusValenciennes forPygidiumMeyen, proposed by Eigenmann, is not adopted here for the reason that the name ofTrichomycterusValenciennes is a well‐established name, is not anomen preocupatum, as Eigenmann imagined, and also as the name ofPygidiumhas been used by Meyen for a quite different fish which has no common features withTrichomycterus.Features used by taxonomists for the species of the genusTrichomycterusare revised.A detailed description ofTrichomycterus rivulatusbased on a study of 387 specimens in 62 series is given. Ten formerly described species are considered as names or synonyms ofTrichomycterus rivulatus.These are:–Trichomycterus incseValenciennes;Trichomycterus gracilisValenciennes;Trichomycterus barbatulaValenciennes;Trichomycterus pictusCastelnau;Trichomycterus eigenmanniBoulenger;Trichomycterus pæyanusCope;Pygidium oroyæEigenmann&Eigenmann;Pygidium quechuorumSteindachner;Pygidium tiraqueFowler;Pygidium atochæAllen.The types of variation ofTrichomycterus rivulatusare described and dis

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1944.tb00219.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY