SPERMATOGENESIS OF LICE 661 



In the dog-louse and in H, consobrinus I have been unable 

 to find the spermatocyte divisions, in the latter case perhaps 

 because my material was scarce ; but in the former case all 

 mitoses were extremely rare. As, however, all the other stages 

 of spermatogenesis in the two forms corresponded closely to 

 those of the horse-louse and of Pediculus, it is logical to infer 

 that the missing spermatocyte divisions will be of the same 

 type. 



In the horse-louse the number of chromosomes in spermato- 

 gonial metaphase plates is nine. Spermatocyte prophases 

 indicate a similar number, but not so clearly. In anaphase the 

 chromosomes are too clumped to count with certainty. In 

 H. consobrinus the spermatocyte prophases show seven 

 chromosomes. In the dog-louse no reliable count was obtained. 



After the telophase of the spermatocyte division of the horse- 

 louse the centrosome appears to double as in Pediculus, and 

 from this double centrosome the double axial filament of the 

 tail of the spermatozoa commences to grow out. At this stage 

 the chromatin of the nucleus appears in a clumping which is 

 very irregular but in which a conspicuous nucleolus is always 

 present (Text-fi.g. i). As the spermatid elongates the nucleolus 

 becomes attached to the nuclear membrane so that it projects 

 partly in and partly out of the nucleus (Text-fig. j). It usually 

 appears near the apex of the spermatid but its position is not 

 definite. As spermateleosis proceeds all the staining material 

 in the nucleus disappears, and with it the nucleolus becomes 

 gradually smaller and also disappears (Text-fig. l). This 

 process does not take place in the dog-louse nor in H. con- 

 sobrinus. In Pediculus we described a deeply-staining 

 body which lies within the nucleus at the posterior end of the 

 heads of fairly late spermatids. This does not occur in any cf the 

 new lice examined, and probably corresponds to the late appear- 

 ance of the nucleolus described here in the horse-louse. 



In Pediculus we described a body which we provisionally 

 called the ' acroblast '. In referring to acrosome formation 

 generally, Gatenby and Woodger (8) state ' according to the 

 account given for Smerinthus by Gatenby (6) and for Pediculus 



