124 0. V m R a t h : 



sowolil bei Ascaris meg. als bei Pyrrhocoris apt. beide letztern 

 Theiliing-en sowohl in der Ei- als 8anienbildung als Reductions- 

 thcilnngen aufzufassen. 



Beinahe gleichzeitig- mit dem eben genannten Werke publi- 

 eirte C. IshikaAva (Nr. 8) seine Arbeit über Spermatogenese, 

 Ovogenese und Befruchtung bei Diaptomus. Nach Ishikawa 

 findet in der Ei- und Samenbildung dieses Copepoden die ge- 

 wiinsclite Reduction bei der letzten Theilung statt. Die wesent- 

 lichsten Resultate seiner Untersuchungen hat genannter Autor in 

 folgenden Sätzen zusammengestellt. 



1) The primary sperm cells correspond exactly with the 

 primary egg-cells. Both contain eight chromatic Clements. 



2) In both cells the eight chromosomcs bccome constricted 

 transversely giving rise to eight duuib-bell shapcd bodies. These 

 arrange themselves in an equatorial zone and l)eginn to divido 

 in such a manner that half of each chromosome goes to one 

 cell and the other half to the other. This kind of cell-division 

 takes place two or three times and the resulting cells form the 

 mother cells of eggs or spcrmatozoa, as the case may be. 



3) These grow considerably; after Avhich. 



4) They begin to divide as before; each chromosome divi- 

 ding transversely. This stage corresponds in the e^g to the 

 formation of the first polar body, which takes place exactly in 

 the sanie manner as that of the first division of the sperm-mother 

 cell. In both cases the original eight chromosomcs become di^i- 

 ded into two, giving rise to the daughter cells also containing 

 eight chromosomcs (Weismann's „Aequationstheilung"). 



5) This is immediately followed by another division, 

 without an intervening resting stage of the nuclei, and by reduc- 

 tion in the original mnnber of chroniosomes (Weismann's „Re- 

 ductionstheilung"). The eight chromosomcs which at first are 

 arranged in a single row become arranged in double rows of 

 four each, and the cell begins to divide in such a manner that 

 four chromosomcs go to one cell and the remaining four to the other. 



By divisions described under Nr. 4 and ö a sperm-mother 

 cell as well as an egg-mother cell increases to four cells, which 

 in case of the former give rise to four spermatozon, while in 

 that of the lattcr a single egg cell with two polar bodies, results 

 (or three when the first polar body divides). 



