FERTILISATION OF THE FOOR OF ANIMALS. 173 



tube containing sea watei-, in whicli egg-s had previously 

 been deposited, was placed in a drop containing sper- 

 inatozoa, the spermatozoa were not attracted into the tul)e. 

 On the other hand, it frequently happened that the sper- 

 matozoa gathered ver}'- thickly into small balls just inside 

 and outside of a tube. The balls wore sometimes O'Ol to 

 0*05 mm. in diameter. It was apparent that, since the balls 

 were only formed at the mouth of a tube, the canse of their 

 formation was to be songht in the filtered sea-water. The 

 phenomenon was found to take place after six successive filtra- 

 tions. A drop of sea-water in which eggs had been deposited 

 was placed upon a slide and a drop containing spermatozoa 

 near it. On joining the drops a large number of small balls 

 were formed in a very few seconds. When vei*y numerous 

 spermatozoa were present the balls became O'l mm. in 

 diameter, containing many thousands of spermatozoa packed 

 together in a dense mass. The following appears to be the 

 explanation of the phenomenon : — From the ovary there 

 come out with the eggs a large number of very small bits of 

 jelly, which are so small that they will (like spermatozoa) 

 pass through ordinary filter paper, and so transparent that 

 one cannot directly see them, A few spermatozoa become 

 attached to each piece of jelly, the presence of which may be 

 inferred from the manner in which the small group of sper- 

 matozoa move about. Owing to the length of a spermatozoon, 

 although its head_ may be embedded in a jelly particle, the 

 tail may remain partly free. The little collections of sper- 

 matozoa thus move about hither and thither in no particular 

 direction. When two such groups come by accident into 

 contact they fuse. Certain of the spermatozoa adhere to 

 both little masses of jelly and lock them together. 'J^iie 

 fused mass combines with other simple and fused masses, and 

 so on. It is by this curious synthetic process that, in a very 

 few seconds, there may be formed a ball as large or larger 

 than an Echinus egg and containing thousands and 

 thousands of spermatozoa, looking black under the micro- 

 scope, and easily seen in a drop of water with the unaided eye. 



