144 Papers from the Marine Biological Laboratory at TorHigas. 



number was never great enough to exclude the advisability of consider- 

 ing the common appearance of more than one rod, a Hipponoe character, 

 as an indication of Hipponoe influence. 



THE EFFECT OF THE INCREASE IN THE ALKALINITY OF 



THE SEA-WATER. 



With an increase of alkalinity of the sea-water, brought about by 

 the addition of -^ NaOH, the plutei obtained were of the Hipponoe 

 type, the increased alkalinity causing little modification. A slight 

 increase of Hipponoe influence is apparent. 



A series of experiments for determining the effect of varying degrees 

 of increase in alkalinity was carried out. I give one table (Table III) 

 showing the effect of the addition of 20 drops ^ NaOH (i drop = T 1 - g - c.c.) 

 to 400 c.c. of ordinary sea-water. The eggs from which the plutei were 

 obtained were placed, immediately after being removed from the 

 ovary and washed, in the sea-water whose alkalinity had been raised. 

 The Hipponoe eggs were fertilized 2^ hours later, in a similar solution, 

 with Toxopneustes sperm. The Toxopneustes eggs w r ere allowed to remain 

 in a like solution for 6 hours and fertilized with Hipponoe sperm. 



After fertilization the eggs were changed to more of the same 

 solution, in which they were kept until it was possible to pour the swim- 

 ming blastulas into ordinary sea -water, which was changed from time to 

 time during the days through which the investigation was in progress. 



TABLE III. Summary of results of cross-fertilization in sea-ivater of increased 



alkalinity. 



[Number of plutei studied, 50. Temperature of water, 29 C.] 



Figures of the skeletons of the Toxopneustes $ X Hipponoe cT cross 

 which had been subjected to the NaOH treatment are shown (plates 

 2 and 3, figs. 29 to 37 ; plate 6, fig. 94) ; of the Hipponoe 9 X Toxopneustes^ 

 cross (38-43). The experiments of 1910 showed no change as the result 

 of the increase in alkalinity. This is due, I believe, to the greater alkalinity 

 of the sea-water over that of the Drevious summer. 



