26 E. E. JUST. 



Three methods were used to obtain cross fertilization : allowing 

 the eggs to stand, treating them with alkali, and subjecting 

 them to concentrated sperm. In each experiment reciprocal 

 crosses 3 were made, but it will be convenient to consider them 

 separately. I shall begin with the Arbacia 9 X Echinarach- 

 nius (?. 



I. Arbacia 9 X Echinarachnius cf. 



1. Arbacia eggs allowed to stand in sea-water upward to thirty- 

 six hours show little development following insemination with 

 Echinarachnius sperm. For example, on July 2 I made an ob- 

 servation subsequently repeated throughout the season : 



July 2. Eggs of Arbacia placed in a finger bowl of sea-water from which two 

 samples were removed at hour intervals, from 8 A.M. to 10 P.M.; one sample 

 inseminated with Echinarachnius sperm, the other uninseminated control. Hourly 

 inseminations were continued during the next day until 4:00 P.M., a final insemina- 

 tion at 6:00 P.M. One lot, 24-hour, showed i per cent, cleavage, its control about 

 o.i per cent. 



Results with shed eggs placed in sea-water without subsequent 

 washing and with eggs thoroughly washed by changing the 

 water repeatedly show slight differences. 



2. With alkali treatment the results are practically negative 

 for the amounts of alkali used ; whenever development followed 

 the per cent, was extremely low. 



July 7, 5:00 P.M. Eggs in 10 c.c. of sea-water plus 2 drops of n/io KOH were 

 inseminated with Echinarachnius sperm. 6:40 P.M. Not a single egg formed a 

 membrane. Later none of these developed. 



3. Treatment with concentrated sperm gave the best results 

 between one and three per cent, of eggs developing. For ex- 

 ample, I quote from a long experiment of July 9. 



5:00 PM. Five drops of dry eggs from one Arbacia were put in each of four 

 watch glasses A, B, C, D. To A, one drop of Echinarachnius sperm suspension 

 added and 5 c.c. of sea-water; to B, one drop of Echinarachnius sperm suspension 

 and after five minutes 5 c.c. of sea-water; to C Arbacia sperm and 5 c.c. of sea-water; 

 D, uninseminated control. A gave i per cent, cleavage; B 2 per cent.; C, 95 per 

 cent. ; and D not one membrane or a cleavage. 



Washing the eggs thoroughly would seem to be beneficial 

 to treatment with concentrated sperm but the data on this I 

 deem at present insufficient to be conclusive. 



On the whole, the cross, Arbacia 9 X Echinarachnius cf is 



