LARVAE OF ARBACIA PUNCTULATA 327 



Hence he argued that, since variability was decreased with 

 decreased rate of development, the extreme variants occurring 

 in the cultures subjected to this lowered temperature would not 

 lie beyond that of those found in the open sea. But in his 

 more rapidly developing cultures the variability would be in- 

 creased beyond these limits; consequently the extreme variants 

 in these solutions would lie in either direction beyond the 

 limits of his normal growth-curve, — a fact which he believes 

 of significance in the establishment of species. He discusses 

 the relative variability of individuals of the same parentage as 

 compared with that of the offspring of different parentage, and 

 finds that of the latter wider and more intense. 



Loeb ('98) reported the accelerating effect of alkalies and 

 the retarding effect of acids upon the early embryonic and 

 larval development of Arbacia. He ascribed the beneficial ac- 

 tion of alkalies to an acceleration and the harmful effect of 

 acids to an inhibition of oxidation processes. This effect was 

 scarcely discernible during the first few hours of development, 

 but by the second and sometimes the third day the larvae sub- 

 jected to the alkaline solution were noticeably in advance of the 

 controls, while the development of those in the acid sea-water 

 was retarded or completely inhibited. 



Herbst ('03), working with a medium of artificial sea- water 

 containing magnesium sulphate and the chlorides of sodium, po- 

 tassium and calcium, found that a slight degree of alkalinity, 

 which might not pass above or below a certain point, was 

 essential to development. The optimum concentration varied 

 in the different genera, and, upon approaching the limits of en- 

 durance, .the individual differences in the offspring of the same 

 parents were made more pronounced. In contrast to the re- 

 sults of Loeb with Arbacia, Herbst found that for Spaerechinus 

 and Echinus the sea-water possessed the optimum concentra- 

 tion of hydroxyl and that addition of alkali caused a retarding 

 of development similar to that which occurred when too little 

 was present. 



Moore, Roaf and Whitely ('05) emphasized the 'steadying 

 action' of the sea-water upon variations in the concentration 



