INITIATION OF DEVELOPMENT IN CILETOPTERUS. 49 



and the next morning several swimming, apparently seg- 

 mented, larvae. The sections show a number of segmented 

 blastulae, but no segmented swimmers. In this case the eggs 

 were left in 3.5 c.c. of 2^ M KC1 + 96.5 c.c. sea-water until 

 after the formation of the second polar body, and were then 

 placed in the oxygen-saturated sea-water, where they were left 

 from one half hour to four hours, approximately. Ordinary 

 "KC1 larvse" were present in all cases, as well as the few seg- 

 mented larva?. Sections show considerable amitosis, and some 

 pretty good di-polar spindles, perhaps a better condition of 

 mitotic figures, in general, than in ordinary KC1 material, and a 

 few blastulse, some practically normal, some abnormal. Many 

 pseudo-blastulae appear, e. g., a large nucleated cell at one end of 

 the larva, with a row of smaller cells at the other end separated 

 from the large one centrally by a cavity. These smaller "cells" 

 do not contain nuclei, but appear to have chromatin scattered 

 in the cytoplasm. The experiment was performed on four dif- 

 ferent days, but only once did any considerable number of seg- 

 mented individuals arise, unless the small, nucleated, isolated 

 cells, appearing in one experiment, were due to cleavage followed 

 by a falling apart of the blastomeres. I did not catch them in 

 process of cleaving, so cannot be sure whether such cleavage was 

 mitotic or mere fragmentation. Because of the infrequency of 

 the result, I do not place much weight on it as a means of inducing 

 cleavage unless in some way the results may be made more 

 uniformly certain. However, the fact remains that oxygen- 

 saturated sea-water used after the eggs have been subjected to 

 the action of potassium chloride solution, appears to affect the 

 eggs quite differently from a second "dose" of potassium chloride 

 itself. It would appear that the oxygen has a somewhat dif- 

 ferent function to perform from that of the potassium chloride, 

 and therefore the use of the one does not prevent the action of 

 the other when one follows the other. But used together they are 

 antagonistic. 



3. Heat and Potassium Chloride. As a companion result of the 

 oxygen-saturated sea-water used after potassium chloride, may 

 be given that obtained when heat and potassium chloride were 

 used together. In both cases there was an increase in swimmers 



