INITIATION OF DEVELOPMKNT IN ( H/ETOPTERl '^. 39 



time. Before the experiment the bottle was brought into the 

 laboratory. During the course of the experiment a stream of 

 oxygen was run through the bottle. Unfertilized eggs were 

 placed in the bottle of oxygen-saturated sea-water, and removed 

 at various intervals, from 10 minutes to 4 hours, to dishes of 

 ordinary sea-water on the table. The effect of the treatment was 

 to induce the formation of a small percentage of polar bodies and 

 swimmers. With even so short an exposure to excess of oxygen 

 as 16 minutes, 23.7 per cent, of the eggs formed the first polar 

 body and 2.7 per cent, formed both polar bodies, but with an 

 exposure to oxygen of 55 minutes 16 per cent, formed both polar 

 bodies. A few eggs gave the appearance of one or two cleavages, 

 but no segmented swimmers were found, and less than I per cent, 

 of unsegmented swimmers. 



H. Temperature Changes, i. Cold. Eggs placed in dishes of 

 sea-water at room temperature and then removed to compart- 

 ments of the ice-chest where the temperature was 9.5 C. or 

 12.5 C. for 15 minutes to 2^ hours, gave a small percentage of 

 polar body formation and also of unsegmented swimmers. The 

 swimmers were of the ordinary type induced by KC1 and de- 

 scribed there as apparently typical of unsegmented larvae. 



2. Heat. The use of heat gave by far the best results with 

 Chcetopterus. I consider the experiments to be described as only 

 preliminary tests, as I did not try the method until the end of 

 the summer, and the supply of eggs was giving out, so that I 

 could not make complete tests by any means. By repeating the 

 experiment a number of times, however, I was able to determine 

 with certainty that heat will not only induce development to 

 unsegmented swimmers in a certain percentage of eggs, but will 

 also bring about the delicate balance of processes concerned in 

 mitotic cleavage of a normal sort. The percentages of swimmers 

 obtained were small, many of the cleavages were abnormal, and 

 nearly all the larvae became abnormal in time, but they demon- 

 strate clearly that an agent other than the sperm can induce the 

 segmentation of the egg of Ch&toptems. It may be that some 

 modification of the method, in temperature or time, will lead to 

 the formation of entirely normal larvae, or perhaps SOUK- added 

 agent will be necessary. The only combination which I at- 



