Sexual Cells on the Development of Echinoicls. 351 



fertilised by the mixed sperm of two or more specimens, in order to 

 get as average results as possible. In the experiments to be sub- 

 sequently described, however, in which the stale ova and spermatozoa 

 were mixed several different times at a few hours' interval with fresh 

 sperm and ova, as often as not only one fresh specimen was used in 

 •each case. 



In the subjoined table are given the results obtained in one of the 

 most complete experiments. In this case parallel series of determina- 

 tions were made, in which the ova and sperm were kept in, and after 

 fertilisation diluted with, respectively tank water from the Aquarium, 

 and pure water collected several kilometres from the shore of the Bay 

 of Naples. 



Time of 

 fertilisation. 



Tank water. 



Pure sea water. 



. Per cent, 

 blastulse. 



Per cent, 

 diminution 

 per hour. 



Per cent, 

 blastulse. 



Per cent, 

 diminution 

 per hour. 





98-5 





96-9 





After 6 hours .... 



95-3 



0*5 



95-6 



0-2 



„ 21 „ .... 



83 -2 



0-8 



97-2 



nil 



n 24 „ .... 



77 '9 



1-8 



92-7 



1-5 



1 „ 27 » .... 



73 2 



1-6 



66 -5 



8-7 



„ 30| „ .... 



55-7 



5-0 



0-25 



18 9 



„ 33 „ .... 



36 -0 



7*9 



o-o 



o-i 



„ 35^ „ 



2-2 



13 5 







„ 46 „ .... 



0-0 



0-2 







It will be seen that the ova survived better in the tank water than 

 in the pure sea water, though in two other similar series of experiments 

 the reverse relationship, which one would naturally expect, showed 

 itself. Of the ova fertilised immediately after shedding, one may see 

 that respectively 98"5 and 96*9 per cent, developed to normal blastulse. 

 On keeping, the ova in the tank water began at first to deteriorate 

 more rapidly than those in the pure sea water, but between the 24th 

 and 27th hours, those in pure sea water suddenly began to fall away, 

 and after 30J hours, only 025 per cent of the ova remained to undergo 

 normal development. The ova kept in tank water, on the other 

 hand, postponed their rapid degeneration till the 27th to the 35Jth 

 hours, or more especially till the 33rd to the 35 Jth hours. In order to 

 show more strikingly the suddenness of the onset of this abnormal 

 development on keeping the ova, another column has been added to 

 each half of the table, giving the percentage diminution of normally 

 developing ova per hour. For instance, after six hours development in 

 tank water, 3*2 per cent, less of the ova developed normally, or, on an 



2 D 2 



