162 J- M;oore, 



Weismann supposes the chromosomes to correspond with his 

 theoretical "Idants", hereditary units of the highest order, yet it is, 

 to say the least, strange that so simple an organism as a Rhizopod 

 should possess more of these structures than the reproductive elements 

 of a man. Taken as a whole, karyokinetic figures are, so to speak, 

 more nearly diagrammatic in plants than in animals. While in the 

 former akinesis is rare, in the latter it is comparatively common, much 

 more common than is generally supposed. There is very little doubt 

 that akinesis has often been evolved from karyokinesis ^) and, when 

 we are on the alert for them, intermediate forms may be found on all 

 sides; while the idea that akinetically dividing cells are necessarily 

 moribund, seems to me to be wholly untenable. At first sight one 

 would naturally suppose akinesis to be the forerunner of the mitotic 

 change, but all more recent evidence points strongly to the opposite 

 conclusion. 



It is difficult to picture what would be the exact result of the 

 introduction of akinesis among spermatids, when considered in the 

 relation to a „Reductions-Teilung" and all that this phenomenon is 

 supposed to imply, because, as I have stated, it is not easy to decide 

 how far the two last divisions of the mammal correspond to those ot 

 the „Reductions-Teilung", yet it seems to me incontestable that whetever 

 equation or halving takes place in the rat must be done by the last 

 hetrotype division (always the most marked of every mammalian series) ; 

 but, in this may be division followed by irregular akinetic multipli- 

 cation of the spermatids, which must, so to speak, make short work 

 of any elaborate process of pro-nuclear equation. 



I may put the case another way. We saw^ that it was impossible 

 to consider the accessory bodies essentials to fertilization, as they are 

 present in some animals and not in others. So far as I can see, 

 exactly the same criticism applies to the reduction division of mammals, 

 for sometimes this process operates directly on the spermatozoa, while 

 at others akinesis intervenes. Of course it may be said that these 

 final mitoses of the mammal, do not correspond to the true „Reduc- 



1) Cf. in Qu. Jour. Micr. Sci. Vol. XXXV. p. 274 etc., and also Freuzel, 

 Archiv für Mikr. Anat. Bd. XXXIX. p. 1—28. 



