摘要:

Summary1. The Rhaetic Pteridophytes mainly belong to living families.2. Several isolated families of seed plants existed in the Rhaetic. A large proportion of the genera of the Rhaetic seed plants are stillincertae sedis.3. The structure of the cuticle of the leaf is held to be an important aid to the classification of Rhaetic seed plants.4. Two zones are distinguishable in the plant‐bearing Rhaetic and Lower Lias of Europe and Greenland—theThaumatopterisZone, corresponding approximately to the Hettangian, and theLepidopterisZone, corresponding approximately to the Rhaetic.5. No flora outside this area can yet be satisfactorily correlated with the Rhae

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1931.tb01024.x

出版商:Blackwell Publishing Ltd    

年代:1931

数据来源: WILEY

摘要:

Summary1. The logistic curve which Pearl has applied to the growth of populations of the fruit fly is the law of an experiment carried out under certain restrictions. The assumptions from which the law can be deduced are assumptions whose biological significance is problematical. Their sociological relevance is obscure. There is no sound reason to believe that the decline in European birth‐rate is the expression of a universal law governing the growth of populations. No known biological data conflict with the view that the declining fertility of European communities is a phenomenonsui generis.2. Occupational, statistics from all countries where the birth‐rate has fallen indicate a differential decline. To estimate the genetic significance of differential fertility existing methods are inadequate, and new methods for the detection of genetic differences in social behaviour are required. There are some indications that differential fertility is an ephemeral feature of present‐day conditions because the decline of the birth‐rate is extending to the labouring classes. On this view civilisation appears to be faced with the alternative of devising new incentives to parent‐hood or facing extinction through a progressive decline of population.3. There is insufficient reason to believe that improvement in infant welfare has significantly diminished the expectation of life in the later age groups—or that it is likely to do so in the immed

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1931.tb01025.x

出版商:Blackwell Publishing Ltd    

年代:1931

数据来源: WILEY

摘要:

SummaryThe review covers the ground of external and internal respiration in insects, but deals neither with quantitative changes in metabolism, nor with the intimate processes of oxidation in the tissues.The general anatomy and histology of the tracheal system are described. The form of the tracheae and their mode of ending in the tissues is extremely varied in different insects and in different organs. The question whether the tracheal endings contain fluid or air and the problem of what forces keep the larger branches filled with gas are discussed in detail. The embryological development of the tracheal system and the nature of the “spiral thread” are briefly considered.The exchange of gases in the tracheal system is effected primarily by diffusion. This is modified by opening and closure of the spiracles (“ diffusion control ”) and by mechanical ventilation of the larger tracheal branches (“ventilation control ”). The mechanism of tracheal ventilation is discussed at length: including the part played by the air sacs and the question whether there is a directed stream of air through the tracheal system.The respiratory movements are controlled by nerve centres, variously situated in different insects; and these centres may be stimulated either by oxygen want or by carbon dioxide excess.The relative importance of the spiracles and the skin in respiration, especially in the elimination of carbon dioxide, is discussed.Under the respiration of aquatic insects the functions of the “blood gills,”“tracheal gills ” and “ cuticular gills ” are reviewed, and the problems connected with the “ hydrofuge ” structures of aquatic insects and the air stores which they carry are considered. The respiration of parasitic insects presents many parallels with that of aquatic forms.The part played by the blood of insects as a carrier of ox

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1931.tb01026.x

出版商:Blackwell Publishing Ltd    

年代:1931

数据来源: WILEY