STUDIES OX THE ECTOPAEASITIC TREMATODES OF .lAPAX. ,S7 



and the thread lies in a very finely granular, weakly staining substance. 

 Then this thread splits into numerous shorter pieces ((/), which 

 gradually separate more and more from- each other, and finally 

 occupy the periphery of the common mass in which they lie imbedded 

 (Ji, ?'). At this stage eacli piece of chromatin has assumed a lozenge 

 shape, and become intersected by small clear spaces, effecting a 

 partial division of it into several parts. It contracts more and 

 more and finally becomes a veritable nucleus (k) having a contain- 

 ing membrane M'ith a few granules of chromatin (chromosomes) 

 inside. The newly foi'med nuclei then repeat the very same 

 changes above described, but how many times it is impossible to tell. 

 The small lozenge-shaped chromatin pieces finally formed then begin 

 to lengthen from one end (in), this time apparently without becoming 

 a veritable nucleus such as is represented in k. The tail continues to 

 lengthen more and more until only a small portion of the chromatin 

 remains as the head, so that the ripe spermatozoon has the form of a 

 long pin, formed bead and tail throughout of chromatin (//) ; and all 

 the spermatozoa derived from a single mother-cell of the last gene- 

 ration form a bundle, with the head imbedded in a common mass 

 of finely granular protoplasm. It may be, however, that the proto- 

 plasm forms an exceedingl}'^ thin laj^er around the head as well as 

 the tail. The spermatozoa seem finally to free themselves from the 

 mass of protoplasm ; for I have sometimes observed similar masses 

 floating in the cavity of the testes (o). In I 1 have figured a stage 

 which does not seem to come in well in the above sei'ies, and which 

 I have observed only rarely. It may perhaps represent a stage m\- 

 medLately prior to the one represented in k and of exceedingly 

 short duration. In it the small nuclei have each a cytoplasm of its 

 own of prismatic shape, and ai'e arranged on the surface of a central, 

 spherical mass of protoplasm, which is wholly destitute of a nucleus. 



