SPERMATOGENESIS OF THE DRAGON-FLY. 277 



3. Synapsis. In general, the leptotene threads are so scattered 

 and tangled throughout the cell that it is impossible to be sure 

 of their exact behavior. In occasional cells of a section where 

 only a few threads remain, some threads can be seen to lie 

 parallel to each other, while other threads are united at one end 

 into V's (Fig. 24). 



4. Synizesis. All the threads drift to one side of the nucleus 

 and what appears to be a continuous spireme is formed. If the 

 leptotene threads paired previously side by side as they seem to 

 do in synapsis, the spireme is formed by the end to end union of 

 such paired threads. At this stage, the spireme thread is double 

 (Fig. 27) and the two component threads are twisted and inter- 

 laced (Figs. 25 and 26). The spireme then becomes denser and 

 thicker, possibly by the contraction of the loops which are 

 closely drawn together near the side of the nucleus. The typical 

 bouquet stage described by many investigators appears. There 

 are in polar views through the loops 24 cut ends and as each loop 

 is doubled back so that it would be cut through twice, the actual 

 number of loops is twelve, which corresponds to the haploid 

 number of autosomes. 



The sex-chromosome is still a round, compact body and is 

 seen best when it lies out near one of the larger loops. As a 

 rule it is obscured in the loops near the nuclear wall. 



The centrosome first appears at this stage and in some cells 

 is divided. In others the two centrosomes are separated though 

 there is no indication of the spindle. A large plasmosome some- 

 times appears in the cytoplasm as early as stage I , but it is more 

 common in this period. Figs. 28 and 29 show the spireme and 

 Figs. 30 and 31 are polar views to show the cut ends. In Fig. 

 29 the sex-chromosome is shown among the loops of the spireme. 



5. Segmentation of the Spireme. -The thickened spireme 

 spreads out and breaks up into parts or segments, which are 

 curved into horse-shoe shape loops. The segments are less 

 than the diploid number, but it is not possible to count them 

 accurately. A segment sometimes shows a split that is pre- 

 sumably the space between two leptotene threads which entered 

 into its composition. That these are the same two threads 

 which paired originally seems indicated in Fig. 32, where the 



