No. 2.] THE ORIGIN OF THE SEX-CELLS. 229 
teric cavity breaking through to the exterior. The hydrorhiza 
appear first as stolon-like outgrowths, later they become 
tubular. 
By lowering the temperature, the period of time for the egg 
laying and ejection of the spermatozoa may be changed. 
Blastomeres separated at the two-celled stage develop half 
planulae. 
BryN MAwr COLLEGE, April 22, 1893. 
