FERTILISATION' OF THE EGGS OF ANIMALS. 



165 



gives a purely mecliaiiical explanation, is probably also correct 

 for the spermatozoa of tlie Ecliinodermata. I therefore agree 

 with Ballowitz' that Dewitz was in error in assuming that the 

 movement of spermatozoa in circles upon surfaces is due to 

 a special stimulus arising from the latter. 



The Fiagellata and Ciliata on meeting with an obstacle 

 receive a mechanical stimulus/ to which they respond by 

 reversing their direction of movement for a while. They thus 

 avoid obstacles. It is evident from what has gone before 

 that the spermatozoa of the Echinodermata do not react in 

 this manner. 



One may now inquire what significance the relations of sper- 



FiG. 4. 



matozoa to surfaces has for fertilisation. Special observations 

 to obtain an answer were made upon the eggs of Echinus. 

 It was found that if spermatozoa be added to eggs which 

 have just been placed in water, spermatozoa at once collect 

 upon the outer surface of the gelatinous coat, and a number 

 can be seen there making the characteristic circles. Others 

 are seen to penetrate the jelly immediately on coming in con- 

 tact with it. It is these spermatozoa which do not rotate 

 upon the gelatinous coat which reach the living egg first. Of 

 those spermatozoa which do rotate it was seen that they 



' Ballowitz, loc. cit., p. 393. 



' Jennings, "On llic Muvcinenls and Motor Reflexes of the Fhigellata and 

 Ciliata," ' Aiiier. Juurn. of Physiology, ' vol. iii, Jan., I'JOO, p. 229. 



