摘要:

Forty‐one species of Rotifera are recorded from the River Sokoto, North Nigeria, and details of their seasonal abundance are given. There is a marked change in the composition of the rotifer fauna of the river when it floods in the single wet season. The cyclomorphosis ofKeratella tropicabegins with the appearance of the species in December. At this stage most individuals lack a left posterior spine. The left posterior spine then grows longer in successive samples until February or March and then decreases to very short lengths in June. The right posterior spine does not vary much throughout the cycle and is always positively correlated with the length of the lorica. The length of the left spine shows varying degrees of correlation with the length of the lorica according to the rate of change of length of the left spine.Brachionus caudatusshows synchronous changes of both its posterior spines, the lengths of which are positively correlated with the length of the lorica. The relation of these findings to the general theories of cyclomorphosis is discussed. The flotation theory of Wesenberg Lund is rejected from application to the species studied. The necessity of considering cyclomorphic phenomena in relation to body size is emphasize

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05861.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY

摘要:

Three new species of cephaline gregarine from lepismatid insects of Ceylon are described in this paper. The relationship of these new species to other species belonging to the same genera is discussed. A list is given of the gregarine species so far recorded from Apterygota throughout the world.

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05862.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY

摘要:

Ringicula buccineais an opisthobranch mollusc with a comparatively large external shell which burrows in muddy sand using its foot and cephalic disc. The latter helps to exclude sand from the mantle cavity, is produced into an inhalant siphon dorsally and is fused with the foot laterally. The gill is reduced and the main pallial water current is an exhalant one. There is no exogyrous caecum.Glands open just within the lips and the buccal cavity contains paired jaws and a reduced buccal mass and radula. Into it open the small salivary glands. The oesophagus has neither glands nor crushing plates. The stomach is large with the oesophagus, intestine and liver ducts opening close together to a thin‐walled anterior chamber, whereas a larger posterior chamber has thick, muscular walls and a cuticularized epithelium. Interstitial copepods and Foraminifera are collected for food and crushed in the triturating region.The rectum and pallial genital oviduct lie in the floor of the mantle cavity. A single duct carries both sperm and ova to the mouth of the cavity a bursa copulatrix and receptaculum are associated with it. The penis is retracted into a sheath which opens on the head and is associated with a prostate gland.Discussion of these aspects of the animal's structure confirms its position as a primitive tectibranch which is specialized for burrowing and also shows affinities with the basommatophoran pulmonate

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05863.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY

摘要:

An account is given of the vascularization of the pituitary stalk and of the associated region of the hypothalamus in the minnow. It is pointed out that, making allowance for the fact that the teleosts are widely separated from the main line of vertebrate ascent, the pattern of this vascularization has something in common with that of a median eminence. A particular feature is the existence of a capillary bed in the floor of the infundibular recess and this is shown to have a close topographical relationship with cells containing granules which are intensely stained by chrome‐alum‐haematoxylin. These is some evidence that these may be secretory cells and that their products pass into the blood stream and into the third ventri

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05864.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY

摘要:

Generalized life cycles of five slug species were ascertained from new data on weights of individual slugs together with information on the seasonal state of their genital organs in conjunction with Barnes&Weil's unpublished data on weights.Arion hortensishatches mainly in January and February, grows through the summer months to become mature in September and October. These adults live through the winter, laying eggs and gradually losing weight and die before July of the following year.The eggs ofArion subfuscusare mainly laid in the autumn (late August and September) and hatch sporadically through the winter. The young slugs grow through the spring to become mature in July and the adults die soon after egg‐laying.Agriolimax reticulatusbreeds throughout the year but the rate depends on the weather and each year there is a period of intense egg‐laying associated with the new spring vegetation, that results in a summer abundance of individuals.Milax budapestensishatches during the autumn and winter, grows through the summer to become mature in late October and November when they mate and eggs are laid in the autumn and throughout the winter. The adults die before July of the following year.Milax sowerbiiprobably hatches in early spring, grows throughout the summer, becomes mature, mates and starts to lay eggs in September, October and November. The adults die soon after egg‐l

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05865.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY

摘要:

A clear distinction must be made between the intralacustrine speciation shown by some groups of African cichlid fishes and the simple specific proliferation shown by others. The former phenomenon is exhibited by several genera but hardly at all by the genusTilapia.Inshore dwelling habits and an algal diet have not had restrictive effects on speciation. In fact it is among inshore species that speciation has been most active.While, partially by exploiting their small size, genera which have given rise to the endemic species flocks of the great lakes have become highly specialized for the exploitation of specific niches, the species ofTilapiahave usually remained large and unspecialized and therefore capable of existing in a variety of environments.Further consideration of the effects of predation supports the idea that it has accelerated rather than retarded the process of speciation.If certain conditions are fulfilled, closely related species can co‐exist throughout life in one habitat, eat the same kind of food and breed in close proximity to each othe

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05866.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY

摘要:

The dental formula ofHistriophoca fasciatais: I 3/2, C 1/1, PC 5 (rarely 6) = 34 to 36. The teeth are rather weak, smooth and distantly spaced. The lower incisors are only half the size of the upper ones and are frequently lost. The lower canines point outward at an angle of 45° from the horizontal. In each half of the jaw, upper and lower No. 1 is the smallest of the postcanine series; Nos. 3 and 4 are the largest; Nos. 2 and 5 are nearly equal. On some skulls the gap between upper postcanines Nos. 4 and 5 is distinctly the widest. The upper postcanines may have a small posterior cusp; the lower ones frequently have both anterior and posterior cusps. In each half of the jaw, upper and lower postcanine No. 1 is single rooted; No. 5 is double rooted; Nos. 2, 3 and 4 are transitional.On one specimen, the third pair of upper postcanines is missing and all of the teeth are unusually small. This skull may be pathological or it may be evidence of the variation to be expected in a declining evolutionary form.Male and female are similar in body size and may reach a length of at least 170 cm. and a weight of at least 95 kg. Cranial measurements of five adult males, one adult female and one adult sex‐unknown are giv

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05867.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY

摘要:

The modes of division and branching of the extrapetrous part of the facial nerve and the presence or absence of communications between its branches and between it and the trigeminal nerve and cervical plexus were studied in nineteen mammalian species. Communications between the facial and derivatives of the mandibular division of the trigeminal were found invariably, but were inconstant in the case of the two other divisions and of the cervical plexus.The possible functional significance of the observations is discussed.

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05868.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY

摘要:

The freshwater medusaLimnocnida victoriaewas found from December 1956 to April 1957 in a pool which becomes separated from the main channel of the River Sokoto during the dry season. The medusae are described and the importance of the number and size of statocysts as a systematic character within the genus is discussed. A map showing the distribution ofLimnocnidain Africa is given.

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05869.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY

摘要:

A description is given of the behaviour of oribatid mites from West Africa and North America in temperature gradients. The results of the experiments may be summarized as follows:—(i)West African species had a tolerance zone of 18° C.‐36° C. compared with 16° C.‐28° C. in North American species.(ii)West African species had an upper critical temperature and an upper lethal temperature of 37° C. and 38° C.‐40: C. respectively, compared with 30° C. and 30° C.‐32° C. respectively in North American species.(iii)Most West African species had a preference for conditions in the 24° C.‐31° C. range, compared with 21° C.‐260 C, in North American species.The differences between the two groups depended very largely on the temperature conditions to which the mites had been exposed before the experiments. Evidence of an avoiding reaction by many mites to extreme temperature conditions in the gradient provides a partial explanation for the seasonal change in the distribution of

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1960.tb05870.x

出版商:Blackwell Publishing Ltd    

年代:1960

数据来源: WILEY