282 NATHAN FASTEN. 



attached at one end, as seen in some of the V's, U's and 8's of 

 Fig. 18. 



The four components of each geminus continue to open up in 

 such a manner as to produce typical X's like those shown in 

 Fig. 19. This transformation marks the end of the post-diplotene 

 stage and the cell is now ready to terminate the growth period 

 by the formation of tetrads. 



Figure 20 shows the pre-tetrad condition. The opposite ends 

 of the X's soon wander towards each other and the middle fusion 

 point becomes effaced. The result is that every one of the X's 

 is converted into four thin strands, having the appearance of a 

 pair of parallel lines with a transverse split in the middle. 



Through a further condensation, each of the four thin strands 

 is modified into a spherical chromosome, thus converting every 

 geminus into a tetrad (Figs. 20 and 21). Following this, the 

 typical bivalent dumb-bells are formed through a fusion of the 

 pairs of univalent chromosomes of the tetrads. This is par- 

 ticularly well shown in Fig. 21. Here, also, the centrosome has 

 divided into two elements and each is seen to migrate away from 

 the other. At the same time the nuclear wall has begun to 

 disintegrate and the cell, in general, has terminated its process of 

 growth . 



A careful study of the various stages of growth shows that the 

 chromatoid body makes its appearance in the pre-synapsis period 

 and persists from then on. A centrosome and an idiozome are 

 clearly visible. As for synapsis, it occurs in parasynaptic fashion 

 in which there is a side-by-side conjugation of the chromosomes. 

 This is similar to what happens in the other decapod Crustacea 

 which I have studied (Fasten, '14, '18 and '24). Komai ('20) 

 has also found parasynapsis in the crustacean Squilla oratorio, 

 de Haan. 



Reduction Division. Following the disintegration of the nu- 

 clear wall, the primary spermatocyte enters the metaphase period 

 (Figs. 22 and 23). The bivalent dumb-bells are lined up in the 

 equatorial plane, and from them the delicate spindle fibres con- 

 verge towards the centrosomes which are located at opposite 

 poles. The single chromatoid body wanders undivided towards 

 one of the poles of the cell. In some instances it lies amongst 



