THE SPERMATOGENESIS OF A DAPHNID, 

 SIMOCEPHALUS VETULUS. 



A PRELIMINARY PAPER. 



ROBERT CHAMBERS, JR., 

 ZOOLOGICAL LABORATORY, UNIVERSITY OF CINCINNATI. 



In Daphnids several generations of parthenogenetic females 

 are followed by a sexual generation in which males are produced 

 together with eggs requiring fertilization in order to develop. 

 These eggs, when fertilized, hatch invariably into females which 

 serve as stem mothers for a fresh series of parthenogenetic 

 generations. 



A study of the spermatogenesis of a Daphnid would therefore 

 be of special interest in deciding the question regarding the 

 specificity of spermatozoa in the determination of sex. 



During the summer of 1912 males of Simocephalus vetulus 

 were obtained in abundance from the fresh-water pools in the 

 vicinity of the Marine Biological Laboratory at Woods Hole, Mass. 



The liquid of Petrunkewitsch and Flemming's fluid (strong) 

 proved to be the best fixing agents for the purpose. 



The sections were stained with Heidenhain's hsematoxylin and 

 also with safranin and light green. 



The immature testis is an elongate body consisting of a solid 

 mass of spermatogonial cells with ill-defined boundaries and 

 enclosed in a thin membranous w r all which is carried out pos- 

 teriorly as the vas deferens. 



The spermatogonial cells are fairly uniform in size. Their 

 nuclei are large and contain one or two nucleoli (Fig. 3, a). 



A constant feature is the presence, here and there throughout 

 the testis, of cells distinguished by their disproportionately large 

 nuclei and nucleoli. They occur in all sizes varying from those 

 of ordinary spermatogonia to giant forms shown in Fig. I . 



In more mature testes numerous regions or islands are dis- 

 cernible especially in the center in which cells may be found in 



