106 NICHOLS — SPERMATOGENESIS ONISCUS ASELLUS LINN. [April 4, 



mlissten wie das in Fig. i dargestellte, waren mir, glaube ich, nich 

 entgangen." 



1893. Brauer. The study of the closely related Phyllopod 

 Artemia was undertaken by the same author with the object of 

 ascertaining whether reduction took place in parthenogeneticaily 

 developing eggs. 



The number of chromosomes in the germinal vesicle is eighty- 

 four, and their structure is quadripartite, /. e., each consists of four 

 spheres. In the first maturation division two of these spheres are 

 separated from the others. After this has taken place the matura- 

 tion may proceed in two different ways. The second polar body 

 may be formed and the elements of the dyad separated, or there 

 may be an abortive attempt to form the second polar body, the 

 chromatin, however, remaining undivided and the elements of the 

 dyad not separated. 



Cleavage and further development of the ^gg may take place in 

 both of the above cases. In the first case it is necessary for this 

 that the second polar body be drawn back into the &gg, where it 

 acts as would a male pronucleus. In the second case the nucleus 

 left within the tgg after the formation of the first polar body, be- 

 comes the cleavage nucleus. In the first case the somatic number 

 of chromosomes is 168, in the second case 84. 



It thus appears that the tetrads of the germinal vesicle are 

 bivalent chromosomes and that the actual reduction may or may 

 not take place. 



1893. Moore published the results of his studies on the reproduc- 

 tive elements in Apus and Branchipus. With regard to Branchipus, 

 the chief stress of the paper is laid upon the relation between 

 karyokinesis and protoplasmic structure, the author believing ** that 

 the divisional phenomena of these cells are intimately related to a 

 protoplasmic structure, which might be fitly described as ' Schaum- 

 plasma,' and one of the initial physical impulses toward meta- 

 morphosis is a fusion of some of the intra-nuclear globules ; and a 

 considerable portion of the complicated karyokinetic figures^ with 

 their centrosomes, pseudosomes and dictyosomes, appear to be the 

 logical as well as the actual consequence of the continuance of this 

 process." 



The question of reduction is not entered upon in much detail. 

 From the nucleus of the resting spermatocyte, however, are shown 

 to arise ten chromosomes of dumbbell-shape. These become 



