1/2 L. B. WALLACE. 



(McClung), unpaired in the spermatogonia, as found in the Or- 

 thoptera. This would include the "chromosome special," de- 

 scribed by de Sinety ; (2) the " chromatin nucleoli " (Montgom- 

 ery), paired in the spermatogonia as found in Euchistus. This 

 would include the "small chromosome" of Anasa, described by 

 Paulmier. Such a classification does not apply in the spider, 

 where the heterochromosomes are similar in appearance and be- 

 havior to those described by McClung as accessory chromosomes, 

 but differ from them in arising as a double element. Button's 

 work on Brachystola plainly shows the accessory chromosome to 

 arise as a single element in the spermatogonia. The hetero- 

 chromosomes of the spider, so far as their double origin is con- 

 cerned, resemble the chromatin nucleoli of Euchistus and the 

 "small chromosomes" of Anasa, but are otherwise different 

 from them. In view of these facts, McClung's term is employed 

 in this paper, and as the accessory chromosomes never fuse to- 

 gether, but only lie in close contact, the term will be used in the 



plural. 



PRIMARY AND SECONDARY SPERMATOCYTES. 



Early in the prophase of the primary spermatocyte the chro- 

 matin is finely distributed on a delicate linin reticulum and the 

 accessory chromosomes retain their individuality (PI. I., Fig. 9). 

 This stage I believe to be comparable to the synapsis, for at this 

 time, or possibly earlier, the pseudo-reduction occurs. In none 

 of my best preparations do I find a massing of the chromatin at 

 one side of the nuclear cavity. Such a massing is found in 

 poorly fixed material, but even then it occurs only in the later 

 spireme stages. In his paper on Peripatas Montgomery has as- 

 serted that in synapsis is accomplished an end-to-end union, in 

 pairs, of entire chromosomes, and that this numerical reduction 

 occurs during the retrogressive stages of the telophase of the last 

 spermatogonic division. Blackman, in his work upon Myriapods, 

 in discussing this point, adds : " It can be stated with the greatest 

 certainty that pseudo-reduction occurs during the telophase of 

 the last spermatogonium and is completed before the reconstruc- 

 tion of the nuclear membrane." From the synapsis stage, repre- 

 sented in Fig. 9, arises the spireme. Like other workers, I find 

 it impossible to state positively that it is segmented from the first 



