the Spermatogenesis in Pentatotaa up to the Formation of the Spermatid. 29 



seen. It is still impossible to count them. But since now, as in 

 the synapsis, several (more than 2) free ends of chromosomes may 

 be noted, we are justified in concluding that there had been no fusion 

 in the synapsis of all the chromosomes into a single mass, nor yet 

 the formation of a single chromatin thread. It is at the height of 

 the postsynapsis (Figs. 78—88) that the individual chromosomes may 

 best be counted; and this count has been made by carefully drawing 

 each loop in such cases where the whole nucleus lay in the plane of 

 the section. These nuclei are shown in the Figs. 78 — 88. In the 

 11 nuclei so studied, the number of the chromosomes was found to 

 be as follows : in 4 cases, 3 chromosomes ; in 5 cases, 4 chromosomes ; 

 in 1 case, 5 chromosomes; and in 1 case 5 chromosomes. Into this 

 count do not enter a large number of nuclei in which chromosomes 

 could not be accurately counted, on account of their being too closely 

 arranged. These counts were made as accurately as possible in order 

 to eliminate all possibility of error, necessitating a study of two or 

 more hours for each nucleus, and I do no hesitate to consider these 

 numbers correct. This count proves, accordingly, that the chromo- 

 somes had undergone a diminution in number during the synapsis, to 

 less that one-half the number of chromosomes present before the 

 synapsis. That is, there were 13 present in the early anaphase, one 

 of the original 14 (of the preceding metaphase) having become the 

 chromatin nucleolus ; in the postsynapsis we find we find 3, 4, 5, or 6 

 chromosomes. But in the postsynapsis we do not find 7 chromosomes, the 

 definitive number present in the spermatocytic divisions, but a smaller 

 number; hence in the synapsis the true (i. e. exactly half) reduction 

 of the chromosomes does not take place, but the number is reduced 

 to less than one-half. Moore ('95, Elasmobranchs) concluded that 

 the reduction of the chromosomes does take place in the synapsis 

 (from 24 to 12); if his observations be correct, then there is an im- 

 portant difference in regard to this point between Elasmobranchs and 

 Pentatoma. The irregularity of the number in Pentatoma (3 — 6) 

 would show that the number of chromosomes at this stage is of no 

 particular morphological importance. 



What had been the nature of the fusion in the synapsis leading 

 to this reduction of the number of chromosomes? Plainly it must 

 have been due to mutual fusions of some of the chromosomes , since 

 there is no evidence of an elimination of them from the nucleus. 

 In the synapsis it can only be determined that a number of chromo- 

 somes is present, their number and relative position cannot be deter- 



