474 M. Louise Xichols. 



nor crescents are to be seen. Their number in the spermatocytes 

 of Talorchestia is eighteen. (PI. 2. T, 10; T, 13.) 



The chromosomes of Hippa, on the other hand, are fonxied not 

 by an end to end union of their components, but by their parallel 

 approach. (PI. 2. Hi, 17.) They are much more numerous than 

 in the lower orders. I have counted sixty in the monaster of Hippa. 

 (Fig. Hi, 20.) A difference in size is also a little more evident, 

 although I have not attempted to arrange them into definite groups 

 according to size, nor to count the number in each group. 



There is always, during the prophases of maturation, an increase 

 of cytoplasm in proportion to the nucleus. This takes place to a 

 much greater extent in the Decapoda than in the lower orders (Hi, 

 14-18; Ho, 4-5), and is accompanied by the appearance in the cyto- 

 plasm of a "N^ebenkern." It is no doubt correlated with the forma- 

 tion of mitochondria and the tail capsule of the spermatid. In the 

 spermatocytes of Homarus and of xVstacus the mitochondrial material 

 is particularly noticeable, forming as it does dense granules in the 

 cytoplasm. (Pigs. Ho, 5; A, 3.) The increase of cytoplasm in 

 Astacus is accompanied by a marked growth in size of the nucleus. 

 This can be observed as early as the synapsis and throughout the 

 maturation stages the cells of Astacus are nearly twice as large as 

 those of Homarus. 



The Male Repkoductive Organs. 



The testis of Idotea, like that of the terrestrial Isopoda consists 

 of three lobes emptying separately into the vas. The testes are 

 also alike inasmuch as \^dthin the lobes the developing germ cells 

 do not present a continuous series but occupy zones rather sharply 

 marked off from each other. PL 3. I, 28. In Oniscus and Por- 

 cellio the zones follow each other in linear fashion (ISTichols, 1902), 

 while in Idotea the arrangement is lateral. 



The upper portion of the vas of the Isopoda is expanded. In the 

 terrestrial forms it is appreciably wider than the lower portion and 

 lined with large secreting cells. In Idotea the difference in diameter 

 is not so great and ordinarily the cells lining the two portions do 

 not differ much in appearance. At times, however, a few cells on 



