72 bulletin: museum of comparative zoology. 



above in detail, seems to me to establish very definitely that the 

 association of paired eliromosomes in the pachytene stages is one in 

 which the members lie side-by-side throughout their entire length, 

 and therefore exliibit parasynapsis. I should further add that while 

 I have not singled out any other members of the complex for individual 

 study, a careful analysis of the other spireme segments and the deriva- 

 tive tetrads indicates that the condition of parasynapsis is realized 

 for the entire series. I was thus able to analyze the stages of the 

 complex as a whole after following the history of the selected indi- 

 vidual pairs, whereas previously I was unable to reach a definite 

 conclusion. 



As to the method of division in the first spermatocytes, the evidence 

 presented indicates that B, always, and A, in most cases, divide equa- 

 tionally, while C divides either reductionally or equationally and with 

 equal frequency by each method. My study of the other tetrads 

 leads me to think that, as a general rule, they divide equationally in 

 the first division. Where the first division is equational the second 

 is regarded as reductional, and we therefore have postreduction. 

 The general rule has its exceptions, however, as already noted in the 

 case of C and possibly sometimes in the case of A. 



b. The Conjugation of Chromosomes. 



1. The formation of leptotcne threads. — The evidence for para- 

 synapsis derived from a study of the postspireme stages, as presented 

 in the preceding paragraphs, has not embraced the actual process of 

 conjugation; and it therefore remains to be demonstrated that a 

 side-by-side conjugation does take place. But it is even more im- 

 portant to show that the conjugants are actually chromosomes, the 

 morphological descendants of the telophase chromosomes of the final 

 spermatogonial division. Figure 21 (Plate 2) shows a side view and 

 figure 22 a transverse (optical) section through the chromosomes of 

 cells nearing the end of the telophase of the last spermatogonial divi- 

 sion. The side view shows the chromosomes already partly diffused, 

 but each one occupies a definite territory, so that there is no question 

 as to their persistent individuality, except for the coalescence of some 

 of the polar granules. But, as I shall point out later, the polar gran- 

 ules do not necessarily lose their identity when they unite into the 

 compound masses. The optical section, figure 22, shows even more 

 plainly the persistent individuality of the chromosomes up to this 



