372 KATHARINE FOOT. 



The above mentioned morphological peculiarity of the chromo- 

 somes of many Hemiptera i. e. the unequal bivalent called by 

 Wilson the X Y chromosome is present in the first spermato- 

 cytes of Pediculus vestimenti and its division is typical the two 

 unequal parts dividing as univalents in the first division. The 

 unequal bivalent is demonstrated in the metaphase stages of 

 Figs. 10, n, 12, and the division of the smaller half of the unequal 

 bivalent is shown in Fig. 13. 



Miss Strobell and I (1914) published a series of photographs 

 showing both the first and second spermatocyte divisions in 

 Euschistus variolarius, Euschistus servus and in two generations 

 of hybrids from E. variolarius by E. servus. A comparison of 

 these photographs of the first spermatocyte chromosomes with 

 the above mentioned Figs. 10-13 will show that the first sperma- 

 tocyte chromosomes of Pediculus vestimenti are of the same type 

 as in the species of Euschistus referred to, and it is therefore 

 quite logical to assume that the second spermatocyte chromo- 

 somes are equally typical though its demonstration is not yet 

 possible. 



In Fig. 1 6 (on the right) is a group of chromosomes from an 

 embryo in an egg at the basal end of the ovary. 



It is not possible to determine the exact number of chromo- 

 somes of this group, as 18, 19 or 20 can be counted. 



The first spermatocyte chromosomes indicate that the somatic 

 number should be ten and in the few spermatogonial groups I 

 have found it possible to identify ten chromosomes; but they 

 are so small and so frequently constricted that the estimate 

 can always be questioned. 



I am convinced that the most favorable stage for an exact 

 interpretation of the louse chromosomes is the first oocyte 

 prophase, but to secure this stage involves a patient search which 

 cannot be undertaken at present. Fig. 18 indicates that it will 

 be possible to find the later prophase stages, for in this preparation 

 the chromosomes are nearly formed, and it ought to be possible 

 to find the slightly later stages in the same locality of the ovary. 

 An early stage of the yolk spheres of the ovary is shown in 

 the photomicrograph of Fig. 16 (on the left). These are chromo- 

 some-like structures, which in the early stages select the chroma- 



