摘要:

Contrary to a recently expressed view very little factual evidence has been brought forward to support the idea that predatory fishes, and especiallyLatesandHydrocynus, have had restrictive effects on speciation among other African freshwater fishes. A considerable body of data supports the view that the effects of these fishes do not differ from those of other predators and that predation has facilitated speciation. Further reasons whyLatesandHydrocynuscannot be considered as having effects different from those of other predators are given.The situation in lakes containing these predators is reconsidered. There is no need to attempt to minimize their effects in Lake Tanganyika where their presence and effects are fully compatible with the existence of a rich endemic fauna. The situation in Lakes Albert and Rudolf is more satisfactorily explained by the brief duration of the existence of the present‐day lakes and by their recent invasion by a fully differentiated Nilotic fauna, than by imagining thatLatesandHydrocynushave restricted speciation.The suggestion thatLatesandHydrocynuswere responsible for the inception of the habit of upstream migration for purposes of spawning is discredited, and what seem to be more probable reasons for the phenomenon are give

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05180.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05181.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05182.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05183.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05184.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

The mandibular joint in ten marsupials and monotremes is described.No dise was found inDasyurus.InTuchyglossus, OrnithorhynchusandSarcophilusfine fibrous strands were observed which are assessed to be remnants of discs. Larger segments of discs were observed in both joints ofMacropus. DidelphysandMetachiruspresented complete discs which were attached to the joint surfaces. All other joints presented complete discs, free from the articular surfaces.In joints without discs or opposite gaps in discs, the articular, membranes were thick. Comparison is made to similar appearances in rabbits following surgical removal or damage to the disc.The significance of the variations in the morphology of the discs and articular membrances is discussed.

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05185.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

This investigation has been carried out in order to estimate the extent to which osteological differences normally used as a basis for generic distinction among certain anurans may be explained on the basis of heterochronous changes in bone formation. Representative species of fourteen Australian genera of the family Leptodactylidae were compared, and an osteological survey was carried out on alizarin transparencies of sexually mature and juvenile specimens. As a basis for description, a little known and somewhat neotenic Western Australian anuran,Glauertia russelliLoveridge, was selected.Bone, as a tissue, is a useful index of heterochronous change. It gives a clear indication of the extent to which the developmental processes leading to its formation have proceeded. It often provides a reliable guide to the degree of general development attained by the time an animal reaches sexual maturity.The study of heterochrony indicates the evolutionary importance of this phenomenon in the establishment of certain species and genera. Skeletal distinctions among the Australian Leptodactylidae are readily explained, even at the generic level, in terms of such time‐axis or heterochronous changes. These, through shortening or lengthening the time of development of particular bones, or by altering the speed of their ossification, lead to differences of phylogenetic significance. The fact that not only individual variations but also specific and generic distinctions may arise in this way in certain groups of animals has an important bearing on problems of their distributio

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05186.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

The larvae of the lernaeocerid copepods are as yet very imperfectly known. To extend the knowledge of their morphology, the larvae ofLernaeocera centropristiPearse, 1947, were re‐examined. The larvae had been discovered on the gills ofCentropristus striatus(L.) in Beaufort, North Carolina. Their adult stage is still unknown. The examination has shown that the larvae are almost identical with the known larvae ofLernaeocera, but also that they are equipped with additional armament at the base of the mouth‐cone. Since the presence of this armament appears to be the main distinguishing feature between the larvae of the generaLernaeoceraandLernaeenicus, and in view of other small distinctions, it is proposed thatLernaeocera centropristiPearse, 1947, should be transferred to the genusLernaeenicus, asL. centropristi(Pearse, 19

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05187.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Near the equator in Uganda, the herbivorous land snail,Limicolaria martensiana, occurs in well‐defined populations. These populations may be very large and the snails may in places occur at exceedingly high densities. The snails breed all the year round, but with two peaks that correspond with the two annual dry seasons. They enter dispause whenever the weather is very dry. The size of adult snails seems environmentally determined and it varies in different populations : the largest snails occur on soil rich in calcium. The shells of the snails are highly variable and polymorphic in colour and pattern. In particular, there is a streaked form that occurs in all populations, and four distinct pallid “dilute” forms. The relative frequency of the forms varies markedly in different populations. Polymorphism is greatest at high population densities and the snails are all streaked where they are rare. Polymorphism can be distinguished in Pleistocene fossil popula

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05188.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Quantitative samples of zooplankton from three lakes in the Kigezi District of Uganda have been studied. The systematics of the zooplankton are considered, and some of the identifications given by Worthington&Ricardo (1936) in a previous study of one of these lakes are revised.Lake Mulehe is the shallowest of the three lakes and contains the largost standing crop of zooplankton. This is in agreement with chemical data which indicato that the supply of nutrient salts in Lake Mulehe is higher than in the other two lakes.In October 1962 the zooplankton of Lake Mutanda was characterized by the relative abundance of three species ofDaphniawhich were not found in the samples from the other lakes, although two of these species were present in Lake Bunyonyi in 1931. Rotifers were sparse in Lako Mutands, but here dominant byTetramastix opoliensis.Lake Bunyonyi was richer in rotifers, but here the dominant species wasKeratella tropica, whilo in Lake Mulehe the dominant rotifer wasSynchaeta pectinata.The zooplankton of Lake Mutanda in October 1962 was similar in composition to that of Lake Bunyonyi in 1931, but in 1962 the zooplankton of Lake Bunyonyi was more like that of Lake Mulehe. The possible causos of this change are discussed.

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1965.tb05189.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY