THE DEVELOPMENT OF FASCIOLARIA. l6l 



however can be explained by the theory of selection, since this 

 method of feeding the young is useful to the species. 



The sterile ova --to whatever cause due have an important 

 influence on development ; indeed, all the facts which I have dis- 

 cussed or mentioned in the preceding pages can be united into a 

 system of correlations, each part of which has antecedents or 

 consequents, or both, traceable to the nutritive ova as the first 

 link in a long chain of events. It is clear that without the sterile 

 eggs cannibalism could not occur. It is equally clear that the 

 larvae prepare for this process, and that they are profoundly 

 modified as the result of it. Thus, to consider first external 

 characters, the frothy, irregular ectoderm of the precannibal 

 period is well fitted for the stretching caused by the ingestion of 

 the eggs, for these produce a distension so great that unless 

 provision were made for it in advance a far larger number of 

 embryos would be destroyed by it than as a matter of fact 

 succumb. 



The immediate results of the ingestion of the eggs are an en- 

 tire change in the shape of the embryo, and a great increase not 

 only in its size, but also in the size and organs of the young. 

 The external kidneys are most clearly correlated with the canni- 

 balism. In this case also we meet with provision, for the excre- 

 tory organs appear, and are more highly developed than in any 

 other gastropod embryo known to me, long before their chief 

 need can be felt, and long before they have reached the highest 

 development which they ultimately attain. The early appear- 

 ance of the external kidneys, which a comparison with other 

 prosobranchs snows to be secondary, brings about a change in 

 their position, for if they developed at the time the velum ap- 

 pears, as they do in Fulgnr (McMurrich), or after this appears 

 as they do in Crcpidula (Conklin), they would not be carried out- 

 wards by this organ, ultimately to hang down from its underside. 

 The early development of the external kidneys is thus a case of 

 ccenogenesis, and their final location on the embryo an excellent 

 example of a conspicuous result due to a remote influence, for 

 although this ultimate position and activity are connected with the 

 egg-swallowing habit, this connection is indirect, since fully-de- 

 veloped external kidneys occur in dwarfed larvae devoid of 



