NOTES ON BRANCH IOBDELLA. 109 



As the spermatocytes become transformed into the spermatid, 

 the chromatin gradually changes from the reticulate state into a 

 compact, homogeneous mass. The spermatid is a small oval- 

 shaped cell attached by the tip end of the head to the blasto- 

 phore. Between the nucleus and the cell wall in the region 

 farthest from the blastophore, there is a body which takes a basic 



FIG. 4. A camera lucida drawing of an ovocyte with the No. 6 comp. ocular and 

 2 mm. objective. 



FIG. 5. Prophase of young ovocyte drawn to the same magnification as Fig. 4. 



Fir,. 6. Metaphase of spermatocyte No. 12 comp. ocular and 2 mm. objective. 



FIG. 7. Metaphase of spermatocyte showing the relation of the spindle to the 

 nucleus, drawn to the same magnification as No. 4. 



stain and is the centrosome or centrosornes of the last spermato- 

 cyte generation. The cells become so very small and the cyto- 

 plasm so much reduced that one can not be certain that there 

 are two bodies ; at this stage the body is much larger than the 

 centrosomes during mitosis. 



The distal portion of the cytoplasm becomes drawn out and 

 forms the tail, at the same time the sperm centrosome elongates 

 forming a connection between the nucleus and tail. This region 

 becomes the middle piece in the adult sperm. The rapid elonga- 

 tion of the tail and nucleus soon renders it impossible to detect 

 the presence of the cytoplasm. During the elongation of the 

 nucleus, it stains more intensely and becomes constricted as if a 

 large number of shallow parallel furrows crossed it at about 90 

 to the long axis of the sperm. The very tip of the sperm during 

 nearly all of these changes remains in connection with the 

 blastophore. 



From the quotations cited from Voigt's interpretations of the 

 spermatogenesis of the European Branchiobdella, it is apparent 

 that there are important differences. In a few instances a struc- 

 ture which I regard as the nebenkern as described by Calkins 

 (p. 289) was seen but this structure had no relation in its mode 

 of origin to the nucleolus nor does it play an important role in 



