Sexual Cells on the Development of Echinoids. 357 



(5) and, lastly, those from the ova and sperm of the freshly opened 

 Echinoids. It is of course impossible to get an exact basis of com- 

 parison for the larvae obtained from one stale and one fresh sexual 

 product. The best possible is to take a mean between the size of the 

 original normal larvae and that of the larvae obtained from the fresh 

 sexual products used for fertilising the stale products. The larvae 

 obtained with both sexual products stale are of course accurately com- 

 parable with the original normal larvae. 



In the accompanying table are given the mean percentage differences 

 in the size of the larvae obtained with fresh and stale products, from 

 the original normal larvae in the one case, and from the mean between 

 the original and the fresh normal larvae in the other two cases. The 

 actual body length measurements of the original normal and fresh 

 normal larvae are also given, these being in micrometer eye-piece scale 

 units. 



Condition of sexual 

 cells. 



Fertilisation made after 





9 lirs. 



24 hrs. 



33 lirs. 



45 hrs. 24 hrs. 



34 hrs. 



Fresli ? , stale $ 



Stale $ , fresh $ 



-0'2 

 + 7'1 

 -2-8 



+ 1:9 

 + 3-7 

 -3 



4 1-1 



+ 10-9 



+" 2-0 



ij 



-1-9 :| -3-6 

 + 1-5 +3-9 

 -15-9 1 -5-2 



nil 

 — 2 ' 7 

 -13 



31-01 



Body lengtli of normal 

 Body length of fresli 



29-94 

 26-12 



30 59 



25-85 



I 



M& 30-72 



30-34 1 30 99 



1 



In the first group of observations given in the table these series of 

 measurements were repeated after keeping the sexual products respec- 

 tively 9, 24, 33, and 45 hours. When both the sexual cells were stale, 

 it may be seen that the size of the larvae was only slightly, if at all, 

 affected, the average variation from the original normal larvae being 

 only 0*2 per cent. With fresh ova and stale sperm, on the other hand, 

 the larvae were considerably increased in size, even those obtained 

 with sperm forty-five hours stale being slightly larger than the mean 

 normal. With stale ova and fresh sperm, there was in three out of 

 the four experiments a distinct diminution in the size of the larvae, 

 this amounting to no less than 15 '9 per cent, in the case of the ova 

 kept forty-five hours. This experiment thus affords a most satisfactory 

 confirmation of the conclusion tentatively put forward in the above- 

 mentioned paper, i.e., it shows that whilst larvce obtained from stale ova 

 and stale sperm are of the same size as those obtained from fresh sexual 

 products, those from fresh ova and stale sperm are distinctly larger than the 

 normal, and those from stale ova and fresh sperm distinctly smaller. 



