studies of Reproductive Elements. 



I. Spermatogenesis, Ovogenesis, and Fertilization 

 in Diaptoimis sp. 



By 



C. Ishikawa, Ph. D., Rieakuhakushi. 



Professor of Zoology, Agricultural College, Imperial University. 



With PL I. 



A. DESCMIIITTVE PART. 



The species of Diaptomn^ on wliicli llie fbllinving olj.'ervationa 

 were made is very abundantly found in an old pond in tlie University 

 oTonnds. Its breeding- orr-urs repeatedly at an interval of about 

 two uK^ntlis during tlie colder half of tlie year. 



1. Testicular Sac. 



])V pxaniining the testis under a microscope, we are struck widi 

 the varietv of celluhu- elements found in it. Near to its two ends we 

 tind cells in active division, while its median part is filled with cells 

 whose nuclei a.re in the resting stage. We can therefore divide the 

 entire sac into different zones just as has been done hy Ed. van Bmcdeii 

 and Jidiny^ and lately by 0. Heiitvig,^''^ with the testis of Ascaris 

 megalocepliaJa. Following tlie example of these luithors we shall 

 speak of the ])lind end as the formative zone, the middle part as tlie 

 growiuff zone, and the part near the vas-deferens as the zone of ripening. 



In the formative zone, the nuclei are toleralily large, and with 



