2O4 MAULSBY W. BLACKMAN. 



of the tetrad. When seen en face this opening is always square 

 or diamond-shaped with the angles directed toward the arm, in- 

 dicating that it is continuous into each arm. 



At the stage represented in Fig. 13, d, the tetrads are often so 

 distorted that the typical form is lost, but upon studying them 

 more carefully it is seen that they are always referable to the 

 same type. Taking d as the type, the more common variations 

 are shown in b, c,f,g, h. At b the formation of the arms, instead 

 of occurring in the plane of the threads, has proceeded in a plane 

 at right angles thereto, resulting in the double V figures first 

 mentioned by Paulmier. At c, h the long arms of the cross have 

 been curved around and nearly brought in contact. Such dis- 

 tortions observed in later stages of tetrads result in a figure simi- 

 lar in shape to a seal ring, the point of double cleavage repre- 

 senting the seal and the long arms approximating to form an 

 apparently closed circle. Fig. 13, e, f, g are but slight or ap- 

 parent modifications caused by viewing the tetrads diagonally or 

 in profile. 



By later changes the arms of the cross figures are much short- 

 ened and the divisions between separate chromatids become very 

 apparent (Fig. 14, <7, b, r). However, this shortening and con- 

 densation continues and these divisions are entirely obliterated 

 and the chromosome becomes first a granular mass and later an 

 apparently homogeneous one. The tetrads even at this stage 

 vary considerably in shape as shown in Fig. 14, d, c,f. The 

 typical form is represented by Fig. 14, d, and by numerous 

 chromosomes in Fig. 15. 



During the prophase the tetrads of each nucleus have not de- 

 veloped synchronously, but at any given time are in various 

 stages of formation (Fig. 11). This phenomenon is very easily 

 explained. On account of the dense massing of the chromatin 

 segment in the karyosphere, but a few elements can separate at 

 one time and it very naturally follows that those first escaping from 

 this body exhibit more advanced development than those arising 

 later. At a short time before the dissolution of the nuclear 

 membrane, however, the more tardy individuals have overtaken 

 their fellows and all now appear as homogeneous bodies exhibit- 

 ing strongly all the chromatin reactions. 



