ON THE PROTOPLASTID BODY, ETC. 333 



which led up to the formation of the ovocytes, nor among 

 those by which the polar bodies were extruded from these 

 ovocytes, but that there were only half as many chromosomes 

 present in these last divisions of the ovocytes as in the 

 divisions before the first ovocyte was formed. Therefore the 

 reduction must have taken place as in plants, during the 

 rest following the division by which the first ovocyte was 

 formed. Brauer (7) came to similar conclusions, both with 

 respect to the ovogenesis of Branchipus, and the spermato- 

 genesis of Ascaris, and I have myself shown in a variety of 

 Mammals and Elasmobranchs, that the reduction of the 

 number of the chromosomes takes place in resting cells, 

 one or two generations before the formation of the sperma- 

 tozoa, as the case may be. Moreover, the long series of 

 structural changes in the resting nuclei, which lead up to 

 the formation of the reduced number of chromosomes, and 

 which I have termed collectively the synapsis, as well as 

 the character of the chromosomes themselves, are so com- 

 plex and peculiar as to leave no doubt that the halving of 

 the number of the chromosomes, or synapsis, among all 

 those animals which possess it, must have had a common 

 origin in the past. Further, it has been shown by Farmer 

 (7) that the structural details accompanying the synapsis 

 among lilies, and more especially those of the chromosomes 

 in the division immediately succeeding it, are extraordinarily 

 similar to those existing at a corresponding period in the 

 evolution of the reproductive cells of animal forms. These 

 similarities constitute a fair basis for the assumption that the 

 process may have been inaugurated before the animal and 

 vegetable ancestry went apart, and has existed ever since. 



We have then something actually before us which, 

 in favouring the assumption of a common origin of the 

 sexuality in animals and plants, actually invades the terri- 

 tory of the protoplastids themselves, because there are 

 among these simple organisms forms which are as truly 

 vegetable in their affinities, as there are others which are 

 animal in theirs ; and the synapsis, which appears to be 

 common to both animals and plants, must have originated 

 somewhere far back in the protoplastid ancestry. 



