INITIATION OF DEVELOPMENT IN CH/ETOPTERUS. 63 



chromosomal cleavage, and cytoplasmic cleavage. But the two 

 were not correlated. The two processes did not occur at the 

 same time, nor in any morphological relation to one another. 

 The problem of inducing both processes to go on at the same 

 rate and in morphological correlation is met by the heat treat- 

 ment. It seems very possible that the question of permeability 

 is concerned not only with the external egg membranes, but that 

 a concentric system of semi-permeable membranes or regions, 

 involving, perhaps, alveolar and nuclear membranes, are im- 

 portant factors. F. R. Lillie ('08) has shown definitely that 

 the ground substance of the eggs of Cluztopterus consists of four 

 concentric layers, differing from one another in density and in 

 aggregation of characteristic granules. If these regions and the 







various membranes must all become permeable and in such 

 manner that entrance and exit of substances can take place at a 

 certain rate, in order that reactions which should be correlated 

 may be set up at approximately the same time, it seems very 

 probable that the power of heat in inducing the most normal 

 results so far obtained with Chatopterus is due in part to the 

 fact that its effect is very quickly felt throughout the egg. (Other 

 agents doubtless permeate more slowly.) In this way regions 

 and membranes deep within the egg may be affected at approxi- 

 mately the same time as the more superficial ones, and thus the 

 reactions which arise, may arise in correlation, and the nucleo- 

 plasmic relations normal for development may be set up in the 

 egg. F. R. Lillie ('12) has concluded from his studies on the 

 effects of partial fertilization in Nereis that "the establishment 

 of normal metabolic interchange between the nucleus and the 

 cytoplasm must be regarded as a fundamental function in 

 artificial parthenogenesis." Any agent, then, which will affect 

 the inner regions of the egg at the same time as the outer, may 

 be expected to have a great advantage over one which is slow to 

 penetrate in that it has a much better chance of establishing 

 normal correlations and therefore normal metabolic interchange. 

 5. Artificial Parthenogenesis Supplemented by Fertilization 

 Loeb ('07) states that sea-urchin eggs fertilized after treatment 

 with hypertonic sea-water do not develop normally, but often 

 show multipolar spindles. 



