NATURAL HISTORY OF CUMIXGIA TELLINOIDES. 215 



grown and sexually mature in one year. I have the impression 

 that they do not survive many years. Rings of growth on the 

 shell show that they usually survive from two to four years, but 

 the amount of growth after the third year is negligible. 



In addition to the summarized data on the rate of development 

 given in Tables I. and II. which are averages, I give the record of 

 actual experiments in Table IV. It will be noted that the rates 

 of development of several lots of eggs at temperatures ranging 

 from 1 8 to 35 C. are given. It is interesting that the increase 

 in rate of development from 18 to 23 C. is much greater than 

 it is from 23 to 30 C. 



The summer temperatures of the water at Woods Hole range 

 from 1 8 to 22 C., the lower temperatures being those of June 

 and late September, the higher being attained in July and 

 August. The optimum temperature for the development of the 

 Cumingia egg appears to be around 25 C. although the egg 

 never experiences this temperature in nature. 



The difference in rate of development of embryos between 

 1 8 and 25 is truly remarkable. One therefore does not speak 

 of the normal rate of development of an embryo without con- 

 sidering the temperature. Because of certain interesting features 

 of this table the writer expects later to describe more in detail 

 the temperature coefficient of development of cleaving eggs. 



POLYSPERMY. 



Eggs spawned according to the method here described are 

 convenient for study because they can be artificially fertilized 

 at will. It is important to use only a drop of concentrated 

 sperm suspension to fertilize a small stender dish of eggs, (in 

 about 40 cc. of water) otherwise polyspermy results and abnormal 

 development follows. As stated above, the Cumingia egg is 

 particularly susceptible to polyspermy and it might be a legiti- 

 mate problem for students of fertilization to undertake to explain 

 why this is so, giving due consideration to Lillie's suggestion, Jour. 

 Exp. Zool., Vol. 14, 1913. 



THE LONGEVITY OF THE GAMETES. 



If Cumingia eggs are allowed to remain unfertilized they 

 ultimately die and disintegrate, though it has been found by 



