Some Points in the Spermatogenesifl of Mammalia. 161 



have liad since they came into existence, it is difficult to believe that 

 one or other of tiiese universal constituents had not better have been 

 dispensed with during tlie abnost endless conditional changes to whicli 

 tliey have been subject, unless such elements of cellular anatomy are 

 essential to the proper manifestation of the vital process. Leaving 

 out of consideration the improbable existence of an anucleate class of 

 protozoa, it is apparent that the only universal constituents of the 

 reproductive cells are those of the somatic animal cells, viz. nucleus, 

 cytoplasm and centrosomes. 



The discovery, in relation to the phenomena of karyokinesis, of 

 the exact halving of the nuclear constituents (chromatin) has paved 

 the way to the supposition that the nucleus is a sort of hereditary 

 store-house of the "ids" and "idants" of future generations. Karyo- 

 kinesis is regarded by Weismann as a mechanical contrivance, whereby 

 the analysis of the germ-plasm goes forward during and after the 

 segmentation of the ovum, the phenomenon of the „Reductions-Teilung" 

 being held to represent the necessary quantitative or numerical equation 

 of the hereditary stuffs in two pro-nuclei before their fusion. 



Accepting this view, one would naturally suppose that karyokinesis, 

 the expression of a complex mechanism by means of which the analysis 

 of the germplasm is brought about, would become more highly deve- 

 loped in the higher animals, in which the necessity for the accurate 

 division of the hereditary stuffs is enormously increased. Facts are 

 however exactly the reverse of this. The karyokinesis of any species 

 is, I believe, nearly always most complete in the first and immediately 

 succeeding segmentation figures, while all through the differentiation it 

 gradually wanes. In seeking for material in which to study this 

 phenomenon one naturally turns to reproductive-cells or to some simpler 

 type of life. The early segmentation of a chick shows good karyo- 

 kinetic figures, but an embryo of nineteen to twent}- days is a poor 

 medium for the exhibition of this phenomenon. Recent investigation 

 into the protozoa has revealed a most elaborately karyokinetic multipli- 

 cation of the gTeat nucleus in many Rhizopods. notably in Euglypha 

 alveolata. and it is worthy of note that in these forms the number of 

 slender chromosomes is very great indeed. 



Interuatiouale Mouatsschrift für Aiiat. u. Phjs. XI. li 



