Spermatogenesis in spiders. 523 



a study of other forms. From Maevia vittata, one would not be able 

 to say whether parasynapsis, that is side by side fusion, took place 

 or whether telosynapsis is the rule. 



Autosomes. 



Pachytene stage. After synizesis, the autosomes expand 

 into the nuclear cavity in the form of thick segmented threads 

 which are loop-shaped with the free ends lying near the accessory 

 chromosome. This pachytene stage usually persists for a long time 

 and forms one of the most conspicuous features of the testis. During 

 this period a noticeable increase in the size of the cell takes place 

 and in late phases the cytoplasm, which before this has been neglect- 

 able, comes into prominence (Figs. 29, 30). No centrosome appears 

 in Maevia at this time. In Figs. 29, 30, we have the general appear- 

 ance of these cells shown. The individual pachytene threads are 

 thick, are more or less regular in outline, and their number is con- 

 siderably reduced from that of the leptotene-threads of the presyn- 

 aptic period. There can be little doubt but that, during the synaptic 

 contraction, there has been a pairing and fusion of the leptotene- 

 threads. Immediately after the pachytene threads have emerged 

 from the first contraction, no trace of a split can be found in them 

 even under tlie highest powers. 



Accessory chromosomes and ctetosomes. 



The behavior of the hétérochromosome elements has been followed 

 with considerable care during the pachytene stage. The accessory 

 chromosome may either appear as a large deeply staining nucleolus 

 (Fig. 30) or we may find two rod-like elements lying side by side 

 (Fig. 29). The free ends of the pachytene-threads are always near 

 the accessory chromosome at this period, but I do not regard this 

 as evidence that there is any relation between the two. It seems 

 more probable that the force which draws the leptotene-threads to 

 one side of the nucleus also acts on the accessory chromosome and 

 when the expansion comes after the contraction, the free ends of 

 the pachytene-threads push the accessory body to one side. 



No trace of the ctetosomes has been found during the pachytene 

 period. In one specimen a densely-staining body was found lying 

 free in the nuclear cavity, as shown in Fig. 30, but further study 

 has made it clear that this body has nothing to do with the cteto- 



