THE SPERMATOGENESIS OF THE MYRIAPODS. 2O/ 



of granular chromatin. Each thread very quickly splits longi- 

 tudinally, thus giving rise to two long slender segments ex- 

 tending parallel to each other. Very shortly after this longi- 

 tudinal split is made, apparent indications of the second cleavage 

 may be seen. The first indication of this is a bending of the two 

 halves of the segment at their middle point. This extension may 

 be in exactly opposite directions when the resulting tetrad is of the 

 typical cross shape or may occur in, such a manner that the two 

 angles are drawn out parallel to each other, in which case the 

 double V figure results. This stage of the two forms of tetrad fig- 

 ures is shown in Fig. 13, a, b. The bending of the two segments 

 soon results in a transverse cleavage at the angles as indicated in 

 Fig- I 3. ^ ^. f > , /* The short processes thus produced 

 elongate at the expense of the length of the quadripartite seg- 

 ment until a cruciform figure is produced, the four arms of which 

 are of about equal length. Each of these arms is traversed by a 

 split extending its entire length and thus producing a diamond- 

 shaped opening in the center of the X figure. Thus it is brought 

 about that the two adjacent halves of contiguous arms are con- 

 tinuous and form one of the four chromatids derived by the 

 double splitting of the chromatin segment (Fig. 14, a). The 

 structure of the tetrad is best seen in Scolopendra in the later 

 stages of tetrad formation when the arms have shortened and 

 when the chromatin granules are more densely grouped together 

 (Fig. 14, a, b, r). In the late prophase the chromosome becomes 

 homogeneous and assumes the four-lobed shape represented in 

 Fig. 14, d, e,f. The diamond-shaped opening at the center and 

 the splits in the arms are entirely obliterated. 



While these fundamental changes have been taking place in 

 the other elements the accessory chromosome has also under- 

 gone some alteration. As it emerges from the karyosphere this 

 element is a homogeneous spherical mass of chromatin. (Fig. 

 1 2). In the late prophase it is no longer spherical but presents 

 the appearance of a rod the two ends of which are constricted 

 (Fig. 1 5). This constriction undoubtedly indicates a longitudi- 

 nal division. 



When its history is considered this divergence in form from 

 the tetrads surrounding it is very readily explainable and is pre- 



