two unequal parts [Figure 36, c), so that the polar ring can 

 be divided into halves, or from it a small part is separated, 

 or the fissure occurs in direct proximity from the ring, 

 not touching it completely. The second fissure divides the 

 small segment approximately at a right angle to the first 

 (Figure 36, d), and the third also divides the large segment 

 (Figure 36, e] . 



Thus, the ovum passes into the stage of four blastomeres 

 (Grube noted that the large segment in many cases is divided 

 earlier than the smaller one) . Of the four segments formed, 

 one is larger than all the others, and it is divided by a 

 fourth fissure which provides the beginning of the fifth 

 segment. The following division is concerned with this last 

 and takes place not along its length, but transversely, the 

 result of which is that the divided fifth segment forms a 

 region in the form of a polar field in the inactive pole 

 of the ovum (Figure 36, f) . The sixth, seventh and eighth 

 fissures again go from the active pole to the polar field of 

 the inactive pole. After the sixth division the polar ring 

 on the inactive pole usually disappears. Grube did not see 

 more than eight meridional divisions, and said that in 

 leeches the blackberry stage characteristic for many animals 

 is absent; in this stage the meridional divisions are replaced 

 by transverse ones. 



At the same time as the division, accomplished by 

 means of fissures, in the ovum of Clepsine the process of 

 separation of the small globules from the large segments of 

 the ovum first described by Grube takes place; these globules 

 Grube called WANDUNGSBALLEN . In his opinion, the wall 

 of the body of the embryo is built from them; "Segments of 

 the yolk" and Wandungsballen are nothing more than the 

 macromeres and micromeres of the terminology of today's 

 embryology. The first small globule, as Grube noted, appears 

 on the active pole after the formation of the first fissure 

 and appears to be situated in this fissure. Judging by time 

 and place of the appearance of this globule, here the 

 discussion does not concern the formation of the micromeres, 

 but the separation of the first polar body. The following 

 small globules, forming on the active pole of the ovum, 

 undoubtedly are micromeres. Grube described their accumula- 

 tion, ascertaining during this that by the increase of the 

 number of fissures the number of micromeres increases also; 

 however, these phenomena do not stand in an indissoluble 



522 



