Studies in Crustacean Spermatogenesis. 473 



it is fairly well-marked in Idotea and also in Astacus (I, 12; Hi, 15- 

 16 ; A, 4). It does not occnr at all in Oniscus. Correlated with this 

 tendency to polarity is the appearance near the center of the cell 

 of a faintly staining body, presumably kinoplasmic in nature as it 

 sometimes shows radiations and at other times minute granules may 

 be seen wathin it. '(I, 12, 13, 16; Hi, 17, 19.) In such cells also, 

 as the chromosomes shorten and thicken, they come to lie close to 

 the nuclear membrane, a comparatively clear space being left in 

 the center. When the centrosomes do not arise within the nucleus, but 

 in the cytoplasm as in Oniscus, the chromosomes remain distributed 

 throughout the nucleus. (PI. 2. O, 3.) 



With regard to the manner of formation of the chromosomes, con- 

 siderable similarity is noticeable between members of the same order. 

 Thus in Idotea, as in Oniscus (iSTichols, 1902), the components of 

 each bivalent chromosome occupy with reference to each other one 

 of three positions, end to end, side by side, or a position intermediate 

 between these giving rise to the form of a crescent. A shape not 

 infrequent in Idotea, but not noticed in Oniscus, is that shown in Figs. 

 I, 13-14, c. Here the components are joined end to end and at 

 their place of junction spread out slightly so as to form an incipient 

 cross. This shape is not uncommon in insects and some other forms. 

 Chromosomes like b in Figs. I, 13-15, clearly produced by the par- 

 allel approach of their components, may form either rings or crescents 

 according to the closeness of the approximation. The chromosomes 

 are more numerous than in Oniscus, it being possible to count as 

 many as twenty-eight in the monaster stage (PI. 2. I, 17), whereas 

 in Oniscus there are but sixteen (Xichols, 1902). It is corres- 

 pondingly more difficult to determine how many of each type are 

 present, but there are without doubt at least as many as three of the 

 parallel conjugating type. (Figs. I, 14, 17.) A side view of the 

 metaphase gives much the same appearance as in Oniscus and the 

 difference between the types is quite evident. (Fig. I, 18.) No very 

 marked difference in size of the chromosomes can be observed in 

 either Oniscus or Idotea, although they are not quite so nearly uni- 

 form in size as those of Talorchestia. In the latter animal they 

 appear to be all of one type, formed by an end to end union ; no rings 



