INITIATION OF DEVELOPMENT IN CILETOPTERUS. 6l 



cytolysis goes on to the destruction of the egg unless checked. 

 Child ('n) suggests that the egg is a cell overloaded with food- 

 stuffs and structural obstacles to metabolism, that therefore 

 increased metabolism is necessary for its further development. 

 To quote him more exactly, "Physiologically the gametes are 

 in the extreme stages of senescence and can be saved from death 

 only by some regulatory change, which permits increased meta- 

 bolism, and more specifically probably increased oxidations 

 and syntheses." 



All the facts seem to point to the conclusion that the reactions 

 concerned in maturation and those in differentiation are some- 

 what different. F. R. Lillie ('n) has shown for Nereis that 

 there may be a separation of the stimuli to the two processes 

 even in the case of fertilization, maturation being induced by 

 contact of the sperm with the egg, whereas differentiation does 

 not follow except with penetration of the sperm within the egg. 

 Loeb ('09) has noted in Asterias forbesii that the agent which 

 causes development may hinder maturation, and has suggested 

 that in eggs in which the entrance of the sperm calls out both 

 maturation and development, the same chemical agent may 

 call out both processes. This proves true for Chatopterus 

 within certain limits, as already noted, but at the same time the 

 evidence points to the presence of two different sets of reactions 

 for the two processes. 



4. Problem of Cleavage. Inasmuch as most agents call out 

 differentiation without cleavage in Chatopterus, and only two 

 so far have induced the formation of segmented larva?, there is 

 the possibility of studying some of the fundamental questions 

 of cell-division here. 



Most writers on cell-division have attacked it mainly from 

 the morphological side, making it a question of asters and centro- 

 somes. Cleavage, according to Boveri, is a matter of the 

 presence of the centrosome and of its normal activity. In 

 Chcetopterus centrosomes may be present, but they do not lead 

 to cleavage necessarily. They may divide to form a group of 

 centrosomes in the astrosphere, or they may not be visible at all 

 in the aster. The mitotic figure is extremely abnormal in the 

 KC1 material, and cleavage is absent. There is certainly a con- 



