58 HARRIETT M. ALLYN. 



A second possibility to account for the effect of the potassium 

 cyanide and the de-aerated sea-water has been suggested, 

 namely, that these agents act as stimulants which are followed 

 by a depressing effect, one acting directly, the other through 

 allowing an accumulation of carbon dioxide. According to this 

 hypothesis potassium cyanide may be regarded as a protoplasmic 

 poison which first stimulates, then depresses. It is to be remem- 

 bered in this connection that no development to swimmers 

 follows maturation brought about by potassium cyanide or by 

 de-aerated sea-water. The de-aerated sea-water under this 

 theory may be thought to act indirectly, by permitting the 

 accumulation of carbon dioxide given off by the egg as a result 

 of the intracellular oxidations. No more carbon dioxide would 

 be given off supposedly, than under normal conditions, but in 

 this case there is no oxygen to keep the balance of processes 

 normal. The accumulation of carbon dioxide might then act 

 as a stimulus., as it is known to do in other cases. Carbon dioxide 

 above a certain amount, however, is toxic to an organism, and 

 after it has reached this amount with the eggs it may act as a 

 narcotic, inhibiting further development. A simple experiment 

 to test this might easily be performed with a stream of carbon 

 dioxide. Thus the potassium cyanide and carbon dioxide would, 

 according to this hypothesis, act first as stimulants, and then as 

 depressants. Just what physiological processes are involved in 

 such "stimulation" is unknown. 



3. Problem of Differentiation. The term differentiation is used 

 here to denote the developmental changes which occur after 

 maturation and which lead, when complete, to the production of 

 swimmers. Cleavage may be omitted in the process of differen- 

 tiation. Cleavage is, of course, essential to the production of 

 normal larvee, but certain differentiations may go on without it, 

 even to the production of swimming larvae. 



Differentiation may be induced in Chcetopterus by a varied 

 list of agents, both physical and chemical. Nearly every agent 

 tried induced either differentiation or maturation or both, and it 

 is probable that the list of possibilities is very extensive indeed. 

 Besides the agents which I have mentioned in this paper, Loeb 

 ('oi) has brought about development in Cliatopterus by the use 



