THE SPERMATOGENESIS OF A DAPHNID. 139 



of the cellular elements in young testes and of the formation of 

 cysts enclosing spermatocytes, all the contents of a cyst being 

 in the same stage of development. He does not describe nuclear 

 changes, giving, as an excuse, the diminutive size of the cellular 

 elements. His figures, showing degenerating cells, are not con- 

 clusive for one might easily confuse synizetic and interkinetic 

 nuclei and possibly different stages of the giant cells with de- 

 generative appearances. Occasional abnormalities do occur in 

 any gonad but in healthy normal specimens studied by me I have 

 been unable to discover degenerative appearances except among 

 spermatids. 



Two classes of spermatids, of which one only produces func- 

 tional spermatozoa, are described by McClendon 1 in his studies 

 in the spermatogenesis of Pandarus sinnatus, a parasitic Copepod, 

 a species which exists only in the sexual state. According to 

 McClendon some of the spermatids are transformed into "nutri- 

 tive spheres." The "spheres " are a constant feature in Pandarus 

 and the proportion formed is very large. On the assumption 

 that spermatids occur in male- and female-producing classes, this 

 condition might possibly disturb the sex ratio of the species. 

 This is not true for I have collected large numbers and have 

 always found the males and females in approximately equal 

 numbers. 



A personal study 2 of the spermatogenesis of Pandarus sinnatus 

 has convinced me that McClendon's "nutritive spheres" are 

 derived not from spermatids but from spermatocytes during 

 interkinesis. If, then, we assume post reduction for the sex- 

 determining factor, a condition which obtains in most forms 

 where a distinct accessory or "sex" chromosome occurs, the 

 formation of the "nutritive spheres" will be from neutral cells 

 and should, therefore, cause no disturbance in the ratio of male- 

 and female-producing sperm. 



In Aphids 3 two classes of sperm are produced in the male 

 differing in the presence and absence of an accessory chromo- 

 some. The class which does not possess the accessory chromo- 



1 J. F. McClendon, Arch. f. Zellforsch., V., 1909. 



2 R. Chambers, Jr. In press. 



3 T. H. Morgan, Proc. Soc. Exp. Biol. and Med., 5, 1908, and Science, Vol. 29, 

 1909. W. von Baehr, Arch. f. Zellforsch., III., 1909. 



