Sexual Cells on the Development of Echinoids. 353 



Time of 

 fertilisation. 



Per cent, 

 diminution per 

 hour. 



Time of 

 fertilisation. 



Per cent, j 

 diminu- 

 tion 

 per hour. 



Time of 

 fertilisation. 



Per cent. | 

 diminu- 

 tion 

 per hour. 



1 



Tank 

 water. 



Pure 

 water. 



Tank 

 water. 



m ; i 



Tank 

 water. I 



Directly. . . . 



(99 -7) 



(98 -8) 



Directly .... 



(100 -0) 



Directly. . . . 



(98 -2) 



After 6 hrs. 



0-7 



0-4 



After 9 hrs. 



1-6 



After 6 hrs. 



0-7 



n 10 „ 



0-6 



0-4 



» 24 „ 



1 '0 



„ 11 „ 



nil 



„ 22 „ 



5-8 



1-3 



„ 33 „ 



6-7 



„ 24 „ 



nil 



5> 31 ,, 



2-2 



8-6 



4 45 „ 



0-8 



„ 32 „ 



11-7 



„ 35 



0-8 



0-2 







„ 36 „ 



0-1 



In this next table the results of four series of observations are in- 

 cluded. In the first two the relative effects of tank and of pure sea 

 water, were again compared. In this case the pure water had a much 

 better preservative effect, the ova undergoing their maximum deteriora- 

 tion some ten hours later than those .kept in tank water. In the 

 remaining two series of observations, the sexual products were kept in 

 tank water, the maximum rate of deterioration being between the 24th 

 and 33rd hours, and the 24th and 32nd hours respectively. .This last 

 experiment is in some ways the most striking one made, as 94*8 per 

 eent. of the ova developed to blastulse until the 24th hour, whilst by 

 the 32nd hour only 0*8 per cent, so developed. 



As a whole, therefore, these observations show a fair amount of con- 

 stancy. The mean times of the period of maximum deterioration in 

 the various series are respectively 34 J, 28f , 22, 14 J, 22, 18, 26 J, 28J, 

 and 28 hours, or, on an average, 24|rd hours after the shedding of the 

 ova and sperm. The reason of this constancy may have been the 

 similarity of the conditions of experiment. Thus all the observations 

 were made in the latter half of March and the first half of April, and 

 throughout the temperature of the water only varied between 13*5° 

 and 15-3°. 



The chief conclusion to be gathered from these experiments seems to 

 me to lie in the comparative suddenness of the onset of the increased 

 rate of deterioration of the sexual cells. Thus in all but two out of 

 the nine experiments, the rate of increase of abnormal development 

 remained at about 1 per cent, per hour till the 20th to the 27th hour, and 

 then became so rapid, that within about nine hours the capacity for 

 normal development had almost entirely disappeared. Thus rapid 

 increase is well shown by the graphic method in the accompanying 

 figure. Here the four most striking results obtained are reproduced, 

 the values obtained in each of the different experiments being dis- 

 tinguished by different signs. 



