330 HOMER W. SMITH AND G. H. A. CLOWES. 



that after 4 or 5 cleavages the alkali cultures are about even with 

 the controls. There is a slight but perceptible decrease of the 

 velocity of division in acid solutions between pH 5.8 and 7.8, in 

 contrast to the Arbacia egg where the .velocity remains practically 

 constant. 



If we consider the limits for eggs transferred to the pH solu- 

 tions at the time of the first cleavage, these limits are pH 5.4 and 

 i o.i. Thus the limits within which the development of Asterias 

 eggs is possible are distinctly on the alkaline side of those for 

 Arbacia eggs. 



In those solutions in which the velocity of development is re- 

 duced below 50 per cent., the quality of cell division in both 

 Arbacia and Asterias eggs is greatly altered. The division of 

 the cytoplasm is apparently restrained before the division of the 

 nucleus, and in consequence the majority of eggs become multi- 

 nuclear. This condition of abnormal division is indicated in Fig. 

 i by the wavy portions of the curves. After two or 3 cleavages 

 of the nucleus without cytoplasmic division the egg usually divides 

 abruptly into more than two blastomeres, but the division is in- 

 variably abnormal and either soon ceases entirely or leads to 

 cytolysis. In some cases it can be observed that the cytoplasm 

 begins to divide but the furrow melts and the blastomeres fuse. 

 The tendency for nuclear division without cytoplasmic division is 

 much more marked in alkaline than in acid solutions. A point is 

 reached on the alkaline side, however, where nuclear as well as 

 cytoplasmic division is completely inhibited. A similar repression 

 of cytoplasmic division without complete repression of nuclear 

 division has been observed with lack of oxygen, the action of 

 chloroform and ether, the action of hypertonic and hypotonic sea 

 water, cold and other agents (12). 



We are concerned here principally with variations in develop- 

 mental velocity which are made manifest in the early history of 

 the dividing egg, during that period of time in which accurate 

 quantitative information can be obtained. It is of interest to 

 consider, however, the effects of longer exposures. A method is 

 not available for expressing these effects quantitatively but a fair 

 idea of the degree of retardation during a 24 hour exposure can 

 be obtained by comparing the general development of the larvae. 



