BLACKMAN: THE SPERMATOGENESIS OF SCOLOPEXDl.'A. 13 



elements, however, does not assume a granular condition, but retains 

 all the characteristics of a chromosome in the metaphase. This is the 

 accessory chromosome. The whole mass of chromosomes at this stage 

 is surrounded by a clear space irregularly bordered by the cytoplasm, 

 but possessing no membrane. Figures 7, 8, represent a later stage in 

 the disintegration of the chromosomes. The chromatin threads are still 

 more granular and have become elongated into much more slender fila- 

 ments. The accessory chromosome is still intact, and is plainly to be 

 distinguished in the loose mass of granular filaments. The nuclear 

 membrane is not yet re-formed. This figure and the one following re- 

 semble very much the synapsis figures of Moore ('95) for elasmobranchs, 

 and those of Montgomery ('98 a ) for Pentatoma. In the material of both 

 these investigators the synapsis, or fusing together of the chromosomes 

 into pairs, is said to be accompanied by an aggregation of the chromatin 

 threads at one side of the nucleus. In both, the pseudo-reduction 

 apparently takes place considerably later than in Scolopendra, viz., 

 after the reconstruction of the nuclear membrane and the formation 

 of the spireme. In Scolopendra there is no true spireme stage, — i. e., 

 a stage in which all the chromosomes are united into one long thread, — 

 unless, indeed, such a condition is present when the chromatin is aggre- 

 gated in the karyosphere during the vesicle stage ; but this seems very 

 unlikely when we consider the subsequent behavior of the chromatin 

 during the prophase of the first spermatocyte. This stage (Figs.>7-10) 

 in Scolopendra is the synapsis stage in the correct sense of the term. 

 The chromosomes in the anaphase preceding are of the somatic number, 

 and in the stages immediately following (Fig. 10) are of the reduced 

 number. During the entire synapsis, which begins in the early telo- 

 phase of the last spermatogonium (Fig. 7), the chromosomes are aggre- 

 gated into a more or less dense mass. On account of this close massing 

 and -of the small size of the cells at this stage it is impossible in S. 

 heros to follow the details of this process as Sutton (:02) has done 

 in Brachystola magna. However, in the stages immediately succeeding 

 synapsis the appearances both in the present species and in S. sub- 

 spinipes leave no doubt as to the truth of the statement that reduction 

 is accomplished by an end to end union in pairs of spermatogonial chro- 

 mosomes (Fig. 11). Such stages are much more common in the latter 

 species, where they were first observed, but they also occur in S. heros. 

 At this stage each of the chromatin segments, which are of the reduced 

 number, is composed of two equal or approximately equal parts joined 

 together. At the point of junction there is a small space, bridged ap- 



