No. I.] THE EMBRYOLOGY OF CREPIDULA. 19 



These figures are but rough averages made from counting 

 the capsules and the eggs in many of the capsules laid by a 

 large number of mature females ; I have no doubt that in 

 another lot of individuals the numbers would be found to vary 

 a little from those given above. In general, however, these 

 figures may be taken as approximately accurate. In all cases 

 the smaller the individual of a species the smaller the number 

 of eggs laid, so that two specimens scarcely ever lay the same 

 number of eggs.^ 



This great difference in the number of eggs laid is the 

 result of the different modes of development in the different 

 species. In no species which is not rapidly increasing or 

 decreasing in numbers are more or less ova produced and 

 fertilized than are just sufficient to insure the continuance 

 of that species in its present numbers. There is no reason to 

 believe that any of these species of Crepidula are rapidly 

 increasing or decreasing in numbers at present ; so far as one 

 can judge, each is just about holding its own. If, therefore, 

 one species produces sixty or seventy times as many eggs as 

 another, it must be that in the one case each fertilized ovum 

 has sixty or seventy times as many chances of reaching 

 maturity as in the other case. The history of the development 



1 By a typographical error in a former paper ('92) it is recorded that " about 

 50 eggs are laid in each pouch or capsule " of C. fornicata. It should read 

 " about 250." 



2 Herrick ('91) showed that the number of eggs laid by the American lobster 

 varies greatly, depending upon the size of the lobster. More recently ('95) he has 

 published an extensive series of measurements of female lobsters and computations 

 of the number of eggs laid by them, from which he constructs the curve of the 

 fecundity of the lobster. He concludes that " the number of eggs produced by 

 female lobsters at each reproductive period varies in a geometrical series, while the 

 lengths of the lobsters producing these eggs vary in an arithmetical series." 



