596 NATHAN FASTEN 



forms the maturation divisions follow each other very rapidly, 

 but are preceded by a long period of synapsis, in which the 

 chromatin filament uncoils and drifts to one pole, where it con- 

 denses. The tetrads originate by two longitudinal splits. Dur- 

 ing the first division, the nucleolus is liberated into the cytoplasm 

 and persists there until the spermatid stage. The centrosomes 

 are not visible at the poles of the spindles. Labbe next takes 

 up the transformation of the spermatid into the spermatozoon. 

 According to him, this occurs in the following way: 



1. In the cytoplasm of the spermatid a vescicle makes its 

 appearance opposite the nucleus. This grows and soon presses 

 against the nucleus. Two openings are found in the vesicle, 

 one distal and the other proximal. The latter rests against the 

 nucleus. The shape assumed by the vesicle varies with the 

 species. It may be spherical, cup-like, cylindrical or irregular 

 in appearance. 



2. The cytoplasm proper is transformed into radiating arms, 

 leaving from behind the nucleus. 



3. The cellular membrane of the spermatid persists as an outer 

 vesicle. 



4. Mitochondrial masses persist in the internal vesicle. 



5. Between the nucleus and the internal vesicle a central body 

 makes its appearance, and this rises somewhat into the canal of 

 the internal vesicle. It stains more heavily than the chromatin 

 elements. 



Labbe regards the internal vesicle as nutritive in its function 

 because of the accumulation of albuminous matter within it. 

 He also regards osmotic phenomena as important in the operation 

 of the outer vescicle. 



Labbe ('04 a) contributed another short paper on the process 

 of spermatogenesis, and especially the tetrad formation in the 

 lobster. After the last spermatogonial division the nucleus 

 contains a coiling spireme and one or two nucleoli. During 

 synapsis, the spireme superficially splits longitudinally and then 

 fragments into segments, each corresponding to one or more 

 chromosomes. Now the longitudinal split becomes effaced and 

 the chromatin threads thicken, and then unite in pairs. The 



