Serual Cells on the Development of Echinoids. 



355 



In all the experiments thus far described, both ova and sperm were 

 kept for similar periods before fertilisation. In order to determine 

 whether the onset of abnormal development depended more especially 

 on the staleness of the one element or of the other, experiments were 

 also made in which either stale ova were fertilised with fresh sperm, 

 or fresh ova with stale sperm. At the same time some of the 

 stale ova were fertilised with the stale sperm, so that properly com- 

 parative results were obtained. These are collected in the subjoined 

 table. 



Time of 

 fertilisation. 



Percentage of normal blastulse. 



? stale. 

 <j stale. 



$ stale, 

 cj fresh. 



$ fresh. 

 $ stale. 



After 9 hours 



a 9 „ 



„ 20 „• 



„ 22 „ 



„ 24 „ 



„ 24 „ 



u 24 „ 



„ 27 „ 



„ 29 .., 



ta 33 „ 



„ 34 „ 



Mean 



8S-0 

 85-6 

 29-0 

 91 -0 

 45 -3 

 70-1 

 94-4 

 73-3 

 2-7 

 10-6 



o-o 



53-6 



81 



•0 



97 -0 



70 



•o 



65-2 



4 



'7 



95 -5 



95 



•0 



93 -0 



87 



•3 



96-2 



87 



•6 



19-7 



95 







81 -1 



67 



■3 



68-6 



94 



•3 



5-9 



48 



•1 



73-6 



23 



•8 



36-0 



68 



•6 



66 -5 



On comparing the three columns, one can see that there is no regu- 

 larity in the figures. In two cases the maximum number of normal 

 blastulse was obtained from stale ova and stale sperm, in four cases 

 from stale ova and fresh sperm, and in five cases from fresh ova and 

 stale sperm. In the last line of the table are given the mean percent- 

 ages of all the observations made. From these one may perhaps con- 

 clude that whilst on an average just as many blastulse are obtained 

 with stale ova as with stale spermatozoa, yet that when both the sex 

 cells are stale, the proportion is slightly less. Probably, however, one 

 is more justified in concluding that within certain limits it is a matter 

 of indifference whether one or other or both of the sex cells is stale. 

 Thus if the last three observations in the table, made between the 29th 

 and 34th hours, be omitted, the average percentages of blastulae 

 obtained in the remaining eight experiments are respectively 72*1, 

 73*5, and 77*0, i.e., nearly as great with both sexual cells stale as with 

 only one. These last three experiments would, however, seem dis- 

 tinctly to indicate that when the sexual cells have reached their period 

 of rapid deterioration, it is a distinctly more favourable condition if 

 only one and not both of the cells be stale. 



