ASYMMETRY IN THE STARFISH. 123 



failure to metamorphose may be due to the absence of the forms 

 of animal food essential for this process. 



III. EXPERIMENTAL INDUCTION OF REVERSED ASYMMETRY AND 

 OF BILATERALITY IN Patina. 



Materials and Methods. 



In all experiments dealt with in this paper the eggs of one female 

 fertilized by the sperm of one male were used both for experi- 

 mental and control lots. Large numbers of fully ripe eggs and 

 sperm are readily obtained in the manner described in the intro- 

 duction to this paper. 



After several preliminary trials it was found that the blastula 

 stage is the one best adapted for the experimental induction of 

 reversals of asymmetry. Consequently all experiments herewith 

 presented were performed upon early, middle, and later blastulae, 

 and early gastrulae. 



The experimental procedure was as follows: An ice box 

 containing a large, flat layer of ice was the only unusual apparatus 

 employed. A single lot of eggs was divided into two, three, or 

 four equal lots, care being taken to avoid crowding. As a rule, a 

 single layer of eggs on the bottom of the dish was found to be not 

 too many to permit of normal development. One lot was always 

 kept as a control, being placed from the time of fertilization on in 

 an unheated room, resting upon a concrete table and shaded from 

 too strong light. The experimental lots contained in covered 

 glass vessels were placed directly upon the block of ice. After 

 about half an hour temperature readings were taken and it was 

 found that the water at the bottom of the dish where the embryos 

 lay ranged from 2 to 3 C., this being about the temperature of 

 the surface of the ice itself. At this temperature all progressive 

 development comes to a complete standstill, but is resumed as 

 soon as the normal growth temperatures are reinstated. In spite 

 of the fact, which will be more fully dealt with in a subsequent 

 paper, that development is inhibited at the experimental temper- 

 atures, the ciliated larvae lived and remained active in some cases 

 for as long as ten days, though kept continuously on ice for the 

 entire period. This circumstance is mentioned here merely to 



