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HOMKK VV. SMITH AN' DC. II. A. CLOWES. 



of alkalies or alkaline salts, such as Na 2 HPO 4 , to sea water in 

 which the eggs were growing caused an increase in the rate of 

 growth in the early as well as the late stages, but larger amounts 

 led to abnormal division. They pointed out that in some eggs in 

 quite alkaline solutions nuclear division occurred without cyto- 

 plasmic division, so that the blastomeres became multi-nucleated. 

 Still larger amounts of alkali inhibited both nuclear and cyto- 

 plasmic division. On the other hand, the smallest amount of acid 

 had only an inhibitive action. There was no tendency for nuclear 

 division without cytoplasmic division ; and with comparatively 

 small amounts of acid cell division was completely prevented. 

 They concluded that the extreme limits of reaction at which cell 

 division is possible lie very close together, and they pointed out 

 that the phosphates and carbonates in sea water have a " steady- 

 ing action " against fluctuations in the concentrations of H- and 

 OH-ions which must be advantageous to cell growth. Subse- 

 quently, Whitley (6) found that small quantities of acid and 

 alkali were very injurious to the developing eggs of the plaice, 

 Pleuroncctcs platessa. No accelerating effect was observed in 

 alkaline sea water, but Whitley concluded that a disturbance of 

 the equilibrium towards the acid side is much more fatal than the 

 opposite. There appeared to be an increase in resistance to un- 

 favorable reactions developed in proportion to the age of the 

 larvse. 



Glaser (7) repeated Loeb's experiments with Arbacia in an- 

 other connection and concluded that accelerated development in 

 alkaline sea water is limited to the development from the blastula 

 to the pluteus, and that the early rate of cleavage is not acceler- 

 ated, and may even be suppressed. Glaser noted the time required 

 for the successive cleavage planes to appear in the majority of 

 eggs in the cultures. By this method a small change in velocity 

 of development would be difficult to detect, though it would be- 

 come manifest if continued to the later stages where its results 

 would of course be magnified. 



Although it had another objective, the excellent work of Medes 

 (8) on the causes of variation in the larvae of Arbacia is of inter- 

 est in this connection. Medes made careful comparative measure- 

 ments on the skeletons of plutei obtained by inseminating and rais- 



