摘要:

The morphology of the mouthparts ofChloeon dipterumL. andBaetis rhodaniPictet is described and the manner of functioning of the mouthparts is interpreted on the basis of their morphology and direct observations of feeding larvae. InC. dipterumthe way in which the mouthparts were used depended upon the nature of the food material. The ways in which the mouthparts ofB. rhodanidiffer from those ofC. dipterumare shown to be consistent with the overall adaptation of the former species to flowing water.

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06169.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Wild house mice supplied with excess food and confined in pens rapidly became grossly overcrowded. The mean body weights at specified ages of mice born when overcrowding was acute have been compared with those of mice born earlier, in order to test the hypothesis that overcrowding depresses body weight. In three of the four pens studied the more crowded animals were lighter, but in the fourth they were heavier. There is evidence of great inherent variability in body weight in the species.

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06170.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

This paper concerns the food of the pine martenMarles martesin the Beinn Eighe National Nature Reserve, West Ross‐shire, between 1956 and 1958. The technique of studying food from droppings and the need for correction factors are discussed. The study is based on 337 droppings.The food eaten was varied both in size and nature but small rodents and small birds formed the bulk of the food at all times of the year. Coleoptera, Lepidoptera, carrion, fish and berries were eaten seasonally. Small prey appeared to be preferred. Ninety per cent of the small rodents eaten were short‐tailed volesMicrotus agrestisdespite the fact that bank volesClethrionomys glareolusand woodmiceApodemus sylvaticuswere probably more abundant and the martens' activity rhythm brought them into contact with all three spec

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06171.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

The characteristics of wave riding porpoises are described showing that the animals use a breaking bow wave in much the same way as a human surf‐rider planes in a breaking wav

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06172.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

The breeding season of the hedgehog extends into late August and early September and lactation may continue very late into the year. The incidence of loss of embryos after implantation is low and is estimated at 3‐3 per cent in the small sample recorded. The minimal duration of pregnancy in this species is thirty‐one to thirty‐two days, with a probable maximum duration of thirty‐nine days. Observations on the rearing of the young and on the handling of the young for experimental purposes are r

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06173.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Clutch size of the kittiwake is influenced by the previous breeding experience of the female and also by the time of laying. Both of these factors play a part in determining the clutch size and the correlation between breeding experience and clutch size is not solely the result of older birds breeding earlier. The clutches laid by females breeding for the first time are, on average, smaller than those laid at the same time by more experienced breeders and are less influenced by the time of breeding. No female breeding for the first time has been found to lay three eggs. There is a correlation between the time of the onset of breeding in kittiwake colonies and the average clutch size. It is suggested that a progressive decrease in the clutch size as the breeding season progresses may be widespread in both passerines and non‐passerines and probably occurs only in species which do not normally have two broods in a single breeding seaso

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06174.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Surveyed over nine years, stable populations ofAncylus fluviatilis, Physa fontinalisandLymnaea peregra, all with annual cycles, showed variation from year to year in mean size and in population density at the breeding season. This variation in adult mean size is about twice as great inL. peregra(i.e. approximately ± 17.5 per cent) as in the other two species. Fluctuations in population densities at breeding can be five‐fold inAncylusandL. peregraand three‐fold inPhysa.Annual variations in assessed productivity (as volumes of molluscan tissue per unit habitat) can be over seven‐fold inAncylus, more than three‐fold inPhysa, and over eight‐fold inLymnaea peregra.With exceptions, there is general agreement between the annual figures for the different species, and they can be correlated with certain of the weather conditions prevailing during the preceding year. Severity of the winter appears the most important climatic cause of these molluscan fluctuations, particularly inPhysaandL. peregra.Annual variations inAncylusseem more closely related to spring sunshine, and a possible trophic basis is suggested for this difference between the species.In relating this to other studies the interaction of external and endogenous factors in controlling life cycles is briefly considered. It is suggested that the plasticity in growth cycles and reproductive behaviour shown by freshwater snails is of fundamental selective value. Measurements of variations in growth and density in molluscan populations are proposed as a means of assessment of annual variations in total organic productivity of fr

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06175.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Certain of the growth stages of the lophophore ofTerebratella (Waltonia) inconspicua(Sowerby), from a shell length of 0.55 mm., are described and figured, so as to elucidate the position of the mouth and the mode of development of the lip of the food groove. The mouth is a small aperture in front of the bases of the first formed pair of filaments. The lip of the food groove is formed by lateral growth from a small preoral lobe. The early lophophore (trocholophous and early schizolophous) is of the broad‐based terebratellacean type set low on the dorsal mantle, and the filaments when extended in feeding are directed anteriorly and ventrally. The structure of the adult lophophore is described. The ciliary feeding mechanism is essentially similar to that described by the author inMacandrevia cranium(Müller) and other brachiopods with plectolophous lophophor

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06176.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Pastry “larvae” were coloured in different ways and offered in randomised samples on a lawn to wild birds. Small adaptive changes provided significant protection and included the following methods of camouflage:— background colour resemblance, disruptive coloration, countershading and disguise—a leaf mimic. General colour seemed of overriding importance in camouflage. Very tentative estimations were made of comparative vulnerability values for various methods of camouflage in relation to this particular experimental arrangement. A rather poor quality leaf mimic, a countershaded model and a disruptively coloured model had an approximately equal advantage over a well‐matched plain standard green model, but the advantage was only equal to and certainly not more than a small colour change. Increased predation pressure enhanced the value of small adaptive advantages. Some evidence was found for the adaptive value of seasonal dimorphism. There was some indication that stable polymorphism might be based upon factors simpler than a balance of harmful and benefic

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06177.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Twenty specimens of a trematode, hitherto undescribed, were found inMacurus fabriciicaught off the coast of Iceland. They are described, figured and named in this paper.

ISSN:0370-2774    

DOI:10.1111/j.1469-7998.1961.tb06178.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY