摘要:

The detailed ultrastructure of the pigment body complex located on the dorsal surface of each intrapigmented megalaesthete in the valves ofCallochiton achatinus(Brown, 1827) is described. The pigment body complex comprises a single, large rhabdomer, surrounded by a number of pigment cells, linked to an adjacent myeloid body which characteristically consists of an area of extensive, complex, lamellate whorls consisting of myelin. The rhabdomer probably has no specific visual function. However, the simultaneous contraction of the myeloid body and the increased pigmentation of the cells surrounding the rhabdomer after long‐term exposure to light suggests that the myeloid body is involved in a mechanism controlling pigment movement which would modify the amount of light penetrating the rhabdome

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1995.tb05133.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A. H. Macpherson suggested that much of the current geographic diversity in Canadian Arctic mammals resulted from isolation in refugia during the Wisconsin glacial stage. This study evaluates the refugium hypothesis, insofar as it applies to NearcticDicrostonyx, by means of a statistical analysis of geographic variation in 13 skull characters. Overall, geographic variation among samples is not significant, althoughD. hudsoniusandD. unalascensisare geographically and morphologically distinct. Some variation in skull shape is correlated with winter temperature. Partitioning tests on other measures of shape variation indicate some discontinuities consistent with the refugial hypothesis. Discrete samples reflect possible refugial populations in northern North America, Eastern Beringia and two southern periglacial refugia, one in eastern North America and at least one in western North America.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1995.tb05134.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

In two bog‐dwelling dragonflies,Somatochlora alpestrisandS. arctica, the influence of oviposition date and temperature upon duration of embryonic development was studied. Egg diapause was facultative. With advancing season, the proportion of diapause eggs increases from 0 to 37% inS. alpestrisand from 0 to 18% inS. arctica.Eggs needed at least 17 to 38 days for development. Hatching curves were temperature‐independent in nearly all experiments but developmental rate increased at higher ambient temperature. InS. arctica, responses of developmental rate to temperature differed in eggs laid on different dates. InS. alpestris, duration of egg development decreased as season progressed. The duration of egg development of non‐diapause eggs and proportion of diapause eggs inS. alpestrisand possibly inS. arcticamay also both be a function of female age at the time of oviposition. The ecological significance of the different development patterns is disc

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1995.tb05135.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY