SPERMATOGENESIS OF PEDICULUS VESTIMENTI. 373 



tin stains and are morphologically so like chromosomes that one 

 is tempted to interpret them as chromosomes which develop into 

 yolk-spheres. 



A series of stages prior to the first spermatocyte metaphase 

 is shown in Figs, i to 9. The centrosomes of the first spermato- 

 cytes (Figs, i to 4) are a feature of these stages which is most 

 marked. The position of these centrosomes in relation to the 

 nucleus is very variable: they are in contact with the nucleus 

 or almost in contact with the periphery of the cell or in any 

 position between these two extremes. In later stages they are 

 frequently divided into two or more, rarely into three, parts. 

 Several of the former are shown in Fig. 7 (the centrosomes of 

 this figure are a little exaggerated by the artist). 



The Development of the Spermatid into the Mature Spermatozoon. 

 The most striking feature in the development of the sperma- 

 tozoon is the duplex character of the tail. Apparently the tail 

 is composed of two distinct and independent filaments, the 

 apparent independence of these filaments being more marked 

 in the earlier stage (Figs. 20-21). One would naturally suppose 

 that one of these filaments represents the flagellum of other 

 forms, but it has not been possible to demonstrate any substance 

 connecting the two filaments, though the fact that even in smear 

 preparations the two are never found widely separated would 

 indicate that they are attached by some connecting substance. 



HISTORICAL SKETCH. 



Certainly no insect has been accused of being the promoter 

 of a greater variety of diseases than the louse and perhaps no 

 accused has been charged with so many crimes on less evidence. 

 Pediculus has been credited with transmitting the following 

 diseases: typhus fever, typhoid fever, recurrent fever, trench 

 fever, tuberculosis, spinal meningitis, plague, leprosy, beri-beri 

 and more than a dozen minor skin diseases. In some of these 

 cases the evidence seems to be confined to the fact that the 

 patient may be infested with lice. 



For typhus fever, recurrent fever and trench fever it has been 

 proved that the lice do in fact transmit these diseases, but details 

 as to the method of transmission are still disputed. It is held 



