94 bulletin: museum of comparative zoology. 



coarser and thicker, displaying at the same time a peculiar tendency to 

 contract to one side of the nucleus, leaving a great clear space across 

 which stretch numerous linin filaments." This grouping of the filaments 

 at one side of the nucleus is in Moore's material characteristic of the 

 period during which pseudo-reduction occurs, but it should not be con- 

 sidered a universal criterion of the synapsis stage. If I understand Moore 

 correctly, the term synapsis is not meant to describe the massing of 

 the chromatin spireme at one side of the nucleus, but to signify the fusing 

 together of the spermatogonial chromosomes into pairs to form the 

 spermatocyte chromosomes. 



My observations upon Scolopendra, as shown in a previoiis paper 

 (Blackman, :03), agree with the later ones of Montgomery (:O0, :01) 

 on Peripatus and Hemiptera, with those of Nichols (:02) on Oniscus, 

 and with the much more convincing ones of Sutton (:02) on Brachystola, 

 in demonstrating that the synapsis, or union of the spermatogonial 

 chromosomes in pairs, occurs during the telophase of the last spermato- 

 gonial division. From observations upon stages immediately succeeding 

 synapsis it is plain that this reduction of the number of chromosomes 

 to form the number characteristic of the spermatocytes is accomplished 

 by an end to end union of entire spermatogonial elements. 



It appears to be the general conception that pseudo-reduction does 

 not occur till a considerably later period. The process is usually said 

 to take place in the early part of the active prophase of the first sper- 

 matocyte, when the chromatin is in the form of a fine spireme. This 

 spireme is said by many writers to be a continuous thread involving all 

 the chromatin of the nucleus, and one of the first changes noticeable in 

 the early prophase is said to be the cleavage of this single thread into 

 a number of segments equal to one half the number of spermatogonial 

 chromosomes going to form it. Such, with slight modifications, is the 

 conception entertained until recently by nearly all cytologists. 



The reduction in the number of chromosomes in Scolopendra is not 

 accomplished in this manner, but occurs, as I have said, during the 

 spermatogonial telophase at the time the elements are becoming granular 

 and elongated. There is at no time a continuous spireme in the cells 

 of this animal. Upon the reconstruction of the nuclear membrane at 

 the close of the long-continued telophase, the chromatin instead of exist- 

 ing in the form of a spireme, consists of a number of distinct segments 

 equal to the number of chromosomes occurring in the succeeding meta- 

 phase. Reduction has already occurred, as will be seen by examining 

 the accompanying figures. The chromatin threads are not closely massed 



