ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1979.tb03387.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1979.tb03388.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

The biology of the very early stages in the upstream migration of the River lamprey has been studied using samples taken from the cooling water intake screens of the Oldbury Power Station in the Severn Estuary. Examination of the numbers of lampreys caught at different times indicate that an increase in freshwater discharge is the predominant environmental factor responsible for initiating the movement from the sea into the estuary, although temperature may also be a contributory factor. The migrants could be separated on the basis of size into typical and praecox forms whose mean lengths during peak abundance were approximately 300 and 240 mm respectively, the corresponding weights being about 53 and 22 g respectively. The typical forms were occasionally found in the estuary as early as July and as late as April, with peak abundance generally being reached in November, whereas the praecox forms were present mainly between January and March. The ratio of typical to praecox forms over the four years of sampling was estimated as 3.3 : 1. In both size categories, the gonadosomic and hepatosomic ratio was greater in females than males. Evidence was also found in the typical forms for a correlation between high numbers and an increased proportion of males. Measurement of a number of different characters, including lengths, weights and condition factors, as well as gonadosomic, hepatosomic and gut ratios, suggest that, although the typical forms enter the estuary over a long period of time, the onset of the changes leading to sexual maturity are more synchronous. A small number of the later typical migrants, however, exhibited different characteristics to those of the majority of the animals comprising this size category. Measurements made on typical animals from Oldbury in November indicate that they can regulate their plasma ions in salinities as high as 70% of full strength sea water.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1979.tb03389.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Using X‐ray and lens weight techniques on wild and known age captive animals age criteria have been established for Grey squirrels in Britain. Adults have fused epiphyses of the radius and ulna and a paired dried lens weight above 76.0 mg. The longevity of Grey squirrels in Britain is considered. Comparisons with similar data from the USA are mad

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1979.tb03390.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

A synchronized seasonal cycle of sexual regression and development is described for the male Grey squirrel in Britain. Sexual development is maximal in December and May and minimal in August. The seasonal cycle can be overriden, but this is exceptional. Comparisons with previous work and the suggestion that the synchronized seasonal sexual cycle is general for Grey squirrels in Britain, and probably America, are made.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1979.tb03391.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

The movements of the isolated buccal mass ofOctopus vulgarishave been investigated. The beaks undergo rhythmic cycles of activity in the absence of applied stimulation and after electrical stimulation of the inter‐buccal connective. Initial opening, closing, retraction and re‐opening phases of movement are described. This cycle of movements is taken to resemble those in the intact animal. Anatomical and electrical evidence identifies the superior mandibular muscle as being partly responsible for the closing and retraction phases of movement. The inferior buccal ganglion determines the sequence of these buccal movements, but modification by sensory feed‐back from the musculature is also implied. The preparation will allow a closer comparison of the control of movement in cephalopods and gastr

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1979.tb03392.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

A new species of clawed toad,Xenopus witteisp. nov. is described from highland areas overlapping the borders of Rwanda, Uganda and Zaire. A comprehensive morphological analysis of the species has been carried out.X. witteisp. nov. is very closely related toX. vestitusand both have a tetraploid chromosome complement (2n= 72), the only examples within the genus. Nevertheless, the two species may be distinguished by easily observed features, including head morphology and dorsal body colours and patterns, and are also identified by their karyotypes and mating calls.Data on distribution, ecology and parasite infection are derived from both museum collections and fieldwork in Central Africa.X. witteisp. nov. is sympatric in parts of its range withX. vestitus, X. laevis victorianusandX. I. bunyoniensis, with up to three of the taxa sharing the same habitats. The implications of potential species interactions are discussed. Experimental hybridization has confirmed the reproductive isolation of the two tetraploid species. Parasitological studies show that they may be distinguished from one another by host specific species of the nematodeChitwoodchabaudiaand from otherXenopusspecies by the absence of the tapeworm genusCephalochlamys. Large scale population movements of theXenopusspecies have apparently occurred in the Central African highlands during the period of available records. Sympatry observed amongst the present day representatives ofXenopusmay have been an important factor in the evolution of these toads sinceX. witteisp. nov. andX. vestitusare interpreted as allopolyploids, the products of interspecies hybridization.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1979.tb03393.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

The principal acoustic characteristics of the mating calls of 12 species and sub‐species of the genusXenopuswere determined:X. laevis laevis, X. laevis petersi, X. laevis victorianus, X. gilli, X. muelleri, X. borealis, X. clivii, X. fraseri, X. ruwenzoriensis, X. wittei, X. vestitus and X. tropicalis. These calls are very specific, especially among species whose hybrids are particularly viable in the laboratory. Twin species have not been discovered. Most of the species emit calls with high harmonic frequencies of 16 kHz; these frequencies reach 80 and 150 kHz inX. I. laevis and X. ruwenzoriensis, the ultra‐sound level. This was a previously unknown phenomenon in the Batrachi

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1979.tb03394.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Gaimardia(Neogaimardia)finlayiPowell 1933 is a member of the little known family Gaimardiidae which collectively have an Australian, New Zealand and sub‐Antarctic distribution.N. finlayinestles amongst algal holdfasts at the bottom of wave‐exposed beaches in New Zealand. It is a small, weakly heteromyarian dioecious bivalve attached by a relatively stout byssus. The mantle and the siphons are exceedingly simple; mantle fusions, other than anterior and posterior to the internal ligament, are of the inner folds only. The siphons are non‐extensible wide openings with few sensory papillae. Each ctenidium comprises an inner demibranch only with no inter‐lamellar and but a few inter‐filamentar junctions. Within the ctenidium large telolecithal eggs are incubated to a crawling, shelled stage of approximately 0–75 mm in length. Sperm were found in the ctenidium of two mature males. The possible storage of sperm and eggs and the incubation of fertilized eggs have survival value for a small bivalve living in a difficult environment.The modifications which suitN. finlayito its mode of life are discussed, but major interest centres around the taxonomic position of the Gaimardiidae. It is concluded that the Cyamiidae and Gaimardiidae are very closely related, but more comprehensive studies on representatives of both families

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1979.tb03395.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY