DEVELOPMENT OF CUCUMARIA ECHINATA 198 
blastula diminishes in size by one-fifth of its diameter, and 
the internal cavity becomes filled with blastocoele jelly. 
Ludwig (22, p. 605) denied the diminution of size in the 
blastula. For my part, I should think an increase of size would 
seem more probable in such a form where the blastula is wrinkled 
while inside the egg-membrane. Des Arts (2, p. 5) observed 
that in C. frondosa the blastula is formed on the third day, 
and that on the fourth day the cells are so multiplied that 
many folds appear on the surface and an irregularly formed 
internal cavity makes its appearance. As late as on the sixth 
day it is still covered with egg-membrane, but it then acquires 
cilia and rotates actively inside the membrane. On the seventh 
day it emerges from the membrane and is then 405 p in diameter, 
and on the next day a thickening at the vegetative pole occurs. 
The same author gives further the results of the influence of 
the temperature upon the embryo. Besides the syneytium- 
formation which usually results by its being put in a warm 
place, the blastula, being accelerated by warmth, begins to 
rotate on the fifth day, and on the next day it casts off the 
membrane and the vegetative pole thickens. The discrepancy 
found between my culture and those of Mitsukuri with 
regard to the growth-rate, as will be stated later on, seems 
to be due largely, if not exclusively, to the influence of tem- 
perature. I cannot therefore lay much stress upon the time- 
record. 
Similarly wrinkled blastulae are reported by Newth (86, 
p. 633) in C. normani and C. saxicola. In these species 
the morula is solid, and the blastocoele first appears during the 
formation of a wrinkled blastula. At the latter stage cilia 
appear and the embryo soon emerges from the egg-membrane 
and begins to rotate slowly at the bottom. The rotation in 
C. normani is counter-clockwise in direction as seen from 
above, while in C. saxicola it is clockwise. The wrinkled 
surface smoothes out before invagination occurs. According to 
Selenka (45, p. 160) the blastula of H. tubulosa acquires 
cilia near the end of cleavage, and at the twentieth hour it 
comes out of the membrane. The blastula of H. floridana 
