NOTES ON BRANCHIOBDELLA. 



107 



around each nucleus, thus differentiating the blastophore from 

 the germ cells" (p. 275). In B. varians (Voigt, p. 314 sq.) the 

 blastophore arises in a similar although not identical manner. It 

 is first seen just as the spermatogonia escape from the testis at 

 which time but two or four cells are associated with it. When 

 the spermatogonia divide, a portion of the protoplasm is not en- 

 closed within the cell wall, although it is directly connected with 

 the. cytoplasm of the cell. The young stages show the blasto- 

 phore more or less irregular in shape, but as the cells become 

 more numerous it is uniformly spherical. It differs in two par- 

 ticulars from the conditions in Lunibncus : (i) it is found in an 

 earlier stage in the coelome ; and (2) the spermatogonia cells are 

 always distinct in outline from the blastophore, while the earlier 

 stage in Lninbricus is more like a syncytium. 



FIG. 3. A camera drawing of a single section of the ovary and nutritive mass. 

 The dorsal granular portion contains a loosely organized nucleus. The ventral non- 

 granular portion is larger in the other sections of it. 



Branchiobdella instabilia repeats in the formation of the blasto- 

 phore the conditions of B. varians. During the division of the 

 spermatogonia the plane of division has a definite relation to the 

 center of the blastophore. A definite spindle is always present 

 with its long axis tangential to the surface of the blastophore, so 

 that a plane passing through the equatorial plate, if continued, 

 would go through the center of the blastophore. When the 



