12 FRANK R. LILLIE. 



ization would be reckoned 500 times more difficult than straight 

 fertilization in the case of franciscanus eggs. In the case of 

 purpuratus where 75 per cent, fertilized with I unit purpuratus 

 sperm and <o.i per cent, fertilized with I unit franciscanus 

 sperm we could say similarly that cross-fertilization was at least 

 750 times more " difficult " than straight fertilization. It is of 

 course doubtful how much validity such a form of expression 

 possesses, but it is probably sufficient to emphasize the enormous 

 difference that actually exists, which a reader who has not worked 

 with the material might otherwise fail to appreciate. 



Attempts were made to overcome the very strong specificity; 

 increase in concentration of the sperm has only a very limited 

 effect as already noted. The influence of increase of temperature 

 and of alkalinity of the sea water was also investigated in both 

 species with strikingly negative results: Temperature (i) Pur- 

 puratus. Samples of eggs of one female were fertilized with 

 sperm of one male franciscanus (10 units strength) at 15 C, 17 

 C, 24 C. and 27 C. with the following percentages of eggs 

 segmenting: 15, 6.3 per cent.; 17, 10.7 per cent.; 20.5, 3.9 per 

 cent.; 24, 3.5 per cent.; 27, 2.2 per cent. (2) Franciscanus. 

 Samples of eggs of one female were fertilized with sperm of one 

 male purpuratus (8 units strength) at 14 C., 17.5 C, 20.5 C., 

 27 C. with the following percentage of eggs segmenting: 14, 

 3 per cent.; 17.5, 6 per cent.; 20.5, n per cent.; 27, <i 

 per cent. 



Alkali. (i) Purpuratus. Sample of eggs were fertilized with 

 franciscanus sperm (10 units strength) in (a) 50 c.c. sea water 

 + 0.4 c.c. N/io KOH, (&) +0.6 c.c. N/io KOH, (c) -f 0.8 c.c. 

 N/io KOH, (d) + i c.c. N/io KOH, (*) + 1.2 c.c. N/io KOH. 

 In none of these was there any increase above the control, and in 

 the last two decided decreases. (2) Franciscanus. A similar 

 series fertilized with purpuratus sperm of 4 units concentration 

 using NaOH instead of KOH; no fertilization occurred in any 

 of the hyperalkaline solutions ; the control showed 0.4 per cent. 

 fertilization. 



