172 A. H. REGINALD BULLER. 



immediately fix; itself in the jelly. This is, indeetl, wliat 

 appears to take place under the microscope. The tail of the 

 spermatozoon then probably adheres to the outer surface of 

 the egg-coat, aud is dragged round and round on it about 

 the conical head, which is gradually pushed forward through 

 the jelly. It may well be these revolutions (the modified 

 spiral of the usual mode of swimming) whicli cause a 

 spermatozoon to bore through the jelly more or less perpen- 

 dicularly to the surface. The fact that the head is of such a 

 shape that when once embedded in the gelatinous coat it can 

 be easily pushed forward, but offers considerable resistance 

 to moving either backwards or sideways, together with the 

 particular consistency of the jelly, may well account for the 

 steady progress forward of the whole spermatozoon in one 

 direction. It seems to me probable that some such explana- 

 tion as the foregoing will be sufficient to explain all that 

 takes place during the penetration of the gelatinous coat. 



It may here be remarked that since the presence of a 

 gelatinous coat doubles the diameter of an egg its presence 

 multiplies the chances of contact with its exterior surface 

 by a spermatozoon four times. Since the more active sper- 

 matozoa, after coming in contact with the jelly, are con- 

 ducted by it to the living protoplasm of the egg, the chances 

 of fertilisation by them is, by the presence of the gelatinous 

 coat, also increased four times. Since, however, a consider- 

 able percentage of the weaker spermatozoa get stuck in the 

 gelatinous coat after entrance, thus not reaching the liviug 

 egg, our estimate of the increased chances of fertilisation 

 must underyfo a large reduction. The first function of the 

 jelly, which surrounds so many eggs, appears to be that of 

 protection, making them distasteful to larger, and unassail- 

 able by smaller, enemies. For the pur})ose of fertilisation its 

 consistency nuist be such as to allow easy penetration by the 

 spermatozoa. 



The ease with which spermatozoa enter and become fixed 

 in gelatinous substances will explain a phenomenon which at 

 first puzzled mo. It was observed that, when a capillary 



