THE DEVELOPMENT OF FASCIOLARIA. 159 



That some of the embryos break down is due, in Fasciolaria at 

 least, to the fact that they have been outstripped in development 

 by their competitors, whose superior strength, traceable to indi- 

 vidual differences in the sizes of the fertile eggs, in the time and 

 places of fertilization, in the ability at various stages to withstand 

 the effects of exposure at low tide, or the jostling and even in- 

 juries to which the capsules are naturally exposed, probably 

 enables these more fortunate ones to set up such lively currents 

 by means of their cilia that their weak relatives are either whirled 

 about until seriously harmed, or are so crowded into the mass ot 

 collected food ova that injury is certain and death probable. I 

 do not believe that it is necessary, therefore, to trace the sterile 

 eggs historically to degenerating embryos, for even if it were easy 

 to see how selection could occur in this particular case, the phys- 

 ical conditions which account for the breaking down of some of 

 the embryos at the present time, were probably always operative 

 and seem to me of themselves to explain the facts sufficiently well. 



That many of the eggs are unfertilized is more difficult to 

 understand. This is true of Fasciolaria, of Neritina (Biitschli, 

 Blochmann), and of Purpura (Selenka). In this last form 

 Selenka was not able to discover a nucleus. The infertile eggs 

 of Fasciolaria do not react to the influence of chemicals, though 

 in some cases when a few drops of ammonia were added to the 

 water Professor Conklin found that a number of eggs formed pro- 

 trusions at one end. I have repeatedly tried artificial fertiliza- 

 tion, with perfectly fresh eggs, in pure sea water, in a mixture 

 of sea water and the albuminous contents of the capsules, or in 

 the pure albumen. In no case did I succeed in finding more 

 than the usual number of segmenting eggs in such collections, 

 and in no case did the undivided ones seem to have attracted the 

 spermatozoa. Since fertilization normally precedes maturation in 

 the gastropod ovum, I conclude that these eggs are imperfect. 



In what does their imperfection consist ? This is a question 

 which I cannot answer. It seems to me, however, that the di- 

 morphism of the spermatozoa may point the way to a solution. 



Meves ('02) described most remarkable differences between 

 the development of the oligopyrene or worm-shaped sperma- 

 tozoa and the eupyrene or ordinary hair-shaped spermatozoa of 



