476 D. H. WENRICH 



an attenuated thread with a longitudinal cleft, and more or less 

 coiled or bent, according to its length. The longitudinal cleft 

 is what has been called the primary longitudinal spht. 



In cell B, a second split is seen at some points, where four 

 threads are visible (e.g., at a). In cell C all of the segments 

 (except no. 1 and the accessory) have the four chromatids, indi- 

 cating that the secondary longitudinal split has become complete. 

 The other cells, D to H, represent the farther progress of chro- 

 matid transformation and condensation, through characteristic 

 tetrad figures, to the metaphase or early anaphase of the first 

 maturation mitosis. As nearly as possible, all of the tetrads in 

 cells D to H have been given the same orientation; those in cells 

 A, B, and C could not be definitely oriented, partly because the 

 synaptic points could not be determined and, in the case of 

 numbers 7, 8, and 9, partly because of lack of space on the plate. 



c. Synapsis. The point to which especial attention should be 

 directed is that all of the autosomes, or euchromosomes, show 

 the same fundamental conditions, whether they be pairs of telo- 

 mitic or atelomitic chromosomes. All come out of the spireme as 

 elongated threads with one longitudinal cleft visible; all develop 

 a second longitudinal cleft at right angles to the first, giving rise 

 to tetrads, each with four chromatids. And since, as is generally 

 believed, each tetrad represents a pair of spermatogonial chro- 

 mosomes, it would appear that each of the spireme segments in 

 cell A represents a pair of chromosomes which have been ex- 

 tended axially and united side-by-side throughout their length. 



I have already shown ('16) how this side-by-side union of 

 attenuated leptotene threads takes place in Phrynotettix. Evi- 

 dence of the same nature for Chorthippus is presented in figures 



1 to 4, plate 3. In figure 1 a nucleus is shown with one double 

 thread (5) — that attached to the accessory — and another thread 

 which is double at the end nearest the accessory (proximal end) 

 but divides distally into two single threads. Numerous single 

 threads are visible in the other parts of the nucleus. In figures 



2 and 3 a considerable number of these partially conjugated 

 pairs of threads are shown. In none of these drawings (figs. 1 

 to 4) was it possible to represent all of the threads because they 



