FERTILISATION OF THE EGGS OF ANIMALS. 169 



osmic acid aud then washed. In the last case the osmic acid 

 turned the eggs brown. The eggs so killed were put in 

 100 c.c. sea-water for halt" an hour and stirred round at 

 intervals. They were then caught in a pipette, placed in a 

 drop on a slide, and spermatozoa added. The radial penetra- 

 tion was quite as clear as in the living eggs. 



From the foregoing observations it seems evident that the 

 radial penetration is not brought about by any special attrac- 

 tion by the living egg, for it takes place equally well with a 

 dead egg. Nor do the facts point to any chemotactic attract- 

 ing substance as causing the phenomenon, for from a dead 

 egg no excretion can take place. Selenka's suggestion that 

 the spermatozoa take a radial course because they make their 

 way through canals, which during the development of the 

 egg contained protoplasmic connections, also does not seem 

 to me a satisfactory explanation. The radial structure of the 

 gelatinous coat after an egg has been a few hours in water 

 is extremely faint, and, so far as one can directly observe, 

 absent at the periphery where the spermatozoa start on their 

 course. Selenka^ admitted that the canals were finer than 

 the width of the head of a spermatozoon. Surely with the 

 swelling of the jelly these canals must be practically filled up. 

 1 have, as already stated, very frequently seen spermatozoa 

 penetrate the gelatinous coat obliquely, often very obliquely. 

 In these cases the spermatozoa could not be makint>- their 

 way through Selenka's canals. Hence we may conclude that 

 the canals, if such there are, are not necessary for penetra- 

 tion. The thick gelatinous dome of a Petromyzou egg, 

 and also, according to Massart,- the jelly around the ovum of 

 the frog, are penetrated radially without the presence of any 

 canals whatever. These various facts point to the conclusion 

 that the penetration of the gelatinous coat in a more or less 

 radial direction by the spermatozoa is not due to canals, but 

 to some other cause. 



The above reflections led me to make experiments to find 

 ' Selenka, loc. cit,., p. 5. 

 ^ M.assail., " Sui ht I'eiiciraliuii, etc.," luc. cit., p. 217. 



