314 T. A. o'donohoe on dimorphism in the 



spermatozoa were undoubtedly found. I will quote one of the.se 

 extracts, which will be enough for my purpose : " A. Gruvel 

 brings together some of the cases of dimorphic spermatozoa in 

 Paludina vivipai'a, Notommata sieboldii, Asellus aquaticus, 

 Pygaera bitcephcda, Staphylinns and Cyhister roesellii " {Journ. 

 R. M. S., 1905, p. 34). 



It now became quite clear to me that the common house pest, 

 the flea, is one of the animals provided with two kinds of sper- 

 matozoa, but further examination has shown that all are not 

 so endowed, but only about 70 per cent. ; in the remaining 

 30 per cent. I find the smaller form only. This smaller form 

 I find in all, and in all it is more numerous than the larger form. 

 The spermatozoa of the flea are very large compared with those 

 of man, whose spermatozoa, according to Schafer, have an 

 average length of about ^^ in. (0'06 mm.). In the flea the 

 larger form is ^V^^^* ^^ A ^^'^- ^^^S (^"^ mvn. to 0'45 mm.), and 

 the smaller form is about half these lengths. 



They can be seen with a 1-in. objective, but a fine yV-in. is 

 required to make out their structure. Both forms are hair-like 

 with sharp pointed heads, the anterior part of which never 

 stains whilst the second part stains well. Both forms are alike 

 as to the heads, but differ in the length and form of the body, 

 which in the smaller form tapers gradually from the head and 

 ends in a fine line, whereas the body of the larger foi-m gradually 

 increases in size and ends in a bulbous swelling. 



The body in both forms is composed of the following three 

 parts : 



1. The membrane proper of the body, extending from the head 

 to the distal end. 



2. An undulating filament which starts from the back of the 

 head and winds around the body externally ; this is visible in the 

 small form throughout the whole length of the body and projects 

 a little beyond, but in the larger form it is lost sight of about 

 half-way and seen again projecting beyond the bulb-like end. 



