STRUCTURE OF THE VERTEBRATE SPERMATOZOON. 491 



enveloping the head becomes also dissolved. In the guinea- 

 pig the large flat head disappears, and that part only re- 

 mains which is seen as a dark band when the head is en 

 profile, as in c and d in Fig. 5. 



The action of SocIcb Bicarb, is somewhat different; in 

 about forty-eight hours the head becomes transformed into a 

 mass of minute globules, as shown in Fig. 10, and after a 

 time these disappear. 



From the foregoing experiments I am justified in con- 

 cluding — 



1st. That the head of the spermatozoon is enclosed in a 

 sheath, which is a continuation of the membrane which 

 surrounds the filament, and connects it to the body, acting, 

 in fact, the part of a mesentery. 



2ndly. That the substance of the head is quite distinct in 

 its composition from the elliptical structure, the filament, 

 and the long body, and that it is readily acted upon by 

 alkalies ; these reagents have no effect, however, on the 

 other part excepting the membranous sheath. 



Srdly. That this elliptical structure has its analogue in the 

 Mammalian spermatozoon ; in the one case the head is drawn 

 out as a long pointed process, in the other it is of a globular 

 form and surrounds the elliptical structure. 



4thly. That the motive power lies, in a great measure, in 

 the filament and the membrane attaching it to the body. 



In my next paper I propose to enter into the structure of 

 the human spermatozoon and that of some of the iu- 

 vertebrata. 



