GERM CELLS IN ASCARIS INCURVA 69 



The chromatin threads then relax from their position about 

 the plasmasome and fill the nucleus with a diffuse lightly stain- 

 ing network, but shortly there appear throughout the nucleus 

 deeply staining granules which inspection shows to be fre- 

 quently paired and lying on parallel threads. Moreover, the 

 ends of a pair are sometimes clearly attached to the respective 

 parts of a double chromatin mass which later history shows to 

 be a half of a bivalent chromosome in process of formation (fig. 

 30). There are no means of identifying these granules with 

 those described in leptotenization but this condition strongly 

 suggests the reversal of the earUer process. Finally the threads 

 become bare of granules, the paired chromatin masses become 

 the bivalent chromosomes; thus it is that the first maturation 

 separates the paired threads of the earlier prophase. Figure 

 31, a, b (two successive sections of the same nucleus) is of a 

 prophase nucleus and it may well be compared with the same 

 stage in spermatogenesis (fig. 36) as here all twenty-one chromo- 

 somes are bivalent (the quadripartite structure is sometimes 

 shown) in contrast to the male nucleus containing seven unival- 

 ent, thirteen bivalent chromosomes and one tripartite group. 



3. The maturation divisions. These have already been de- 

 scribed in the preliminary report. Figure 32, a and b show ana- 

 phase plates from the first division and figure 35 a metaphase plate 

 of the second division; in both cases there are twenty-one chromo- 

 somes including the microsome. Figure 33 a and b shows 

 chromosomes from two successive sections of a metaphase 

 plate of the first division in side view after fixation in Bouin's 

 fluid which is favorable for a study of the forms of the individual 

 chromosomes. Not all chromosomes are figured as they are 

 too closely massed, but all cross shaped forms have been included 

 and it will be noted that there are three large chromosomes and 

 one small one of this type, while in spermatogenesis only two 

 conspicuously large cross forms or double V's are. present (fig- 

 ure 18 a and c show the receding V-shaped halves of these chromo- 

 somes) so it is not improbale that the third cross represents the 

 long X-component now mated with another of its kind. Figure 

 34 of the same stage after osmic fixation shows the dividing 

 microsome. 



