Studies in Crnstaeean Spermatogenesis. 469 



With regard to the homologies of this spermatozoon as compared 

 with others of the same order, the dark sphere is no donbt the cen- 

 trosome and the tail filament its derivative. The region in which 

 the sphere lies is therefore the middle-piece and the striations may be 

 compared to those visible in the spermatid of Hippa. (Fig. Hi, 24.) 

 This spermatozoon differs from the others inasmuch as the middle- 

 piece is not so well marked and part of the cytoplasm remains 

 surrounding and anterior to the nucleus. 



Fig. P. 7 represents an abnormal spermatid in which the nucleus 

 has failed to condense, while the centrosomes are broken into granules. 



The spermatozoa of the Isopoda are characterized by their aggre- 

 gation into bundles bound together in a common sheath. Distinct- 

 ness of cell boundaries is very early lost between the young sperma- 

 tids. In Oniscus I have sometimes seen in this syncytial proto- 

 plasm bodies staining more or less darkly and showing some tendency 

 to form threads. It seems quite possible that they corespond to the 

 mitochondria of the Decapoda and that the long threads which soon 

 arise in the syncytial protoplasm originate from them. In Oniscus 

 I was unable to make out middle-piece and centrosome, but in Idotea 

 they may occasionally be seen (PL 2. I, 22-25), although it is 

 not apparent that the middle-piece arises from any previously present 

 mitochondrial body. 



The behavior of the nucleus is somewhat different in the two forms. 

 In Idotea the chromatin very early leaves the center of the nucleus 

 and is massed in irregular clumpSi at its periphery. (Figs. I, 19-20.) 

 The irregidar masses next merge together at one pole, while the 

 rest of the nucleus becomes attenuated. (PI. 2. I, 21-22.) The 

 cap-shaped nuclear mass, as it elongates, encloses this attenuated por- 

 tion of the nucleus, which is finally reduced to a mere vacuole or 

 breaks up into a number of smaller vacuoles distributed through the 

 substance of the nucleus. (Figs. I, 23-25.) In Oniscus on the 

 other hand the chromatin is at no time massed around the peripheiy, 

 but is transformed into a network of great delicacy and without 

 vacuoles. Probably this network holds in its meshes a more fluid 

 substance which gradually so changes its character as to stain more 

 and more deeply. Although in both Oniscus and Idotea the nucleus 



