564 SUMMARY OF CURRENT RESEARCHES RELATING TO 



as an aid to anatomy and cytology to embryological study as a causal 

 analysis of the actual process of development. 



Beginning with asexual reproduction and its modes, the author points 

 out that it occurs (especially as proliferation and division) in very 

 favourable nutritive conditions, and also (especially as sporulation and 

 gemmule-forming) in the reverse conditions, of reduced metabolism and 

 depression. There is a synergy or functional interdependence in the 

 organism, in part sustained by hormones ; differentiation is the structural 

 side of the division of labour, and implies a certain degree of senescence ; 

 there are, as Child has emphasized, dominant correlations and subordi- 

 nate correlations ; there are gradations of metabolic intensity along 

 certain lines. When the strictness of correlations is relaxed or the 

 intensity of the dominant function slackened, a part of the body may 

 recover autonomy in its manifestations, some degree of physiological 

 isolation occurs, the parts in question recover their capacity of all-round 

 metabolism, and thus asexual multiplication becomes possible. The 

 relaxing of correlation may come about in many ways, e.g. by the part 

 being removed by growth to a distance from the centre, or by unfavour- 

 able environmental conditions which affect the most differentiated parts 

 most seriously. There is a similar system of correlations in the single 

 cell, but it is a condition of the survival of a part that it should have a 

 nucleus. 



Many investigations point to the origin of germ-cells from early 

 blastomeres freed from any share in differentiation, but the cause of the 

 early isolation is unknown. While recognizing that Woodruff and others 

 have by special care extended the asexual multiplication of Ciliata for 

 many years, Brachet holds to the view, suggested by Maupas, that there 

 is a natural limit to asexual multiplication. In this connexion he refers 

 to the interesting case of Ctenodrilus, which was observed for fourteen 

 years, and did not exhibit in that period more than asexual multiphcation. 

 Eventually Monticelli discovered by accident a large number of sexually 

 mature individuals. 



In describing the structure of the ovum (a common diameter in 

 mammals is yV m™-)' the author notes that the term alecithal is never 

 (juite accurate, and that while the distinction between nutritive deuto- 

 plasm and formative protoplasm is very useful, there are cytoplasmic 

 granulations which it is difficult to classify. Attention is directed to 

 the unique work of Faure-Fremiet on the ovum of Ascaris megalocephala, 

 which traces the chemical linkage between the substances found in the 

 oogonium and those which are elaborated in the oocyte. The histo- 

 genesis of the spermatozoon does not begin until the spermatocyte has 

 reached the condition of maturation-equilibrium. There seems to be no 

 exception to the rule that the spermatogonium of the last generation 

 gives rise by two spermatocytic divisions to four spermatids which 

 become four spermatozoa. Along with Henneguy, Prenant, and others, 

 the author declines to accept the view that the chromosomes are perma- 

 nent and continuous from one cell-generation to another. In regard to 

 maturation, he would distinguish between certainties, such as the 

 numerical reduction of the chromosomes in the course of the maturation 

 of the sex-cells, and conclusions which require further study, such as the 



