€60 H. GRAHAM CANNON 



formed spermatozoa at the thicker end nearer the vas deferens. 

 The position of a cell is thus to some extent an indication of 

 the stage of its maturity. In smear preparations this orderly 

 arrangement is obliterated, and hence it appears to me it would 

 be an easy matter to overlook the unequal spermatocyte 

 divisions in such preparations, even if they were demonstrable, 

 unless their presence were suspected. 



Another aid in working out the spermatogenesis is the develop- 

 ment of the cytoplasmic inclusions, especially the mitosome, 

 pari passu with the maturation stages. It is significant that 

 Miss Foot does not mention or figure the mitosome which is 

 so conspicuous in the later stages of spermateleosis. 



From the examination of the new louse material it is clear 

 that the course of spermatogenesis in the three species observed 

 is, in its main features, the same as that in Pedi cuius 

 corporis and Pediculus capitis as described by 

 Doncaster and myself, and does not agree with the process as 

 described by Miss Foot. This fact is in itself strong indirect 

 evidence in support of our original description. 



The testes of the three species examined were all similar to 

 those of Pediculus, those of H. consobrinus being some- 

 what more pear-shaped and less ovoid. The arrangement of 

 the follicles of cells was the same in all cases, the spermato- 

 gonia being at the free end and the mature spermatozoa being 

 found at the broader end at the entrance to the vas deferens. 

 A conspicuous mitosome is formed in the spermatid by the 

 coalescence of the mitochondria as in Pediculus. In the 

 horse-louse all stages of the single spermatocyte divisions were 

 found, and these were, in all essentials, closely similar to those 

 in Pediculus. The metaphase spindle is always eccentric, the 

 main part of the cell being occupied by the mitochondrial 

 mass. During anaphase the spindle elongates very considerably, 

 and one pole, with its centrosome, is carried outwards from the 

 main body of the cell on a long finger-like projection extending 

 outwards to a distance of the diameter of the cell. This 

 process, with its contained chromosomes, breaks away from 

 the body of the cell, forming a minute ' polar body-like ' cell- 



