I 56 O. C. GLASER. 



dermal primitive kidneys are homologous, and possibly all ecto- 

 dermal primitive kidneys are, but certainly not all external 

 kidneys. The occurrence of unicellular or multicellular accessory 

 external kidneys in different regions of embryos already so well 

 endowed with excretory organs as Fasciolaria shows that the 

 embryological measuring rod which has been so carefully applied 

 to these larval structures of molluscs is less accurate than some 

 of the investigators who have used it for the discovery of alleged 

 detailed relationships. 



III. THE ORIGIN OF THE HABIT OF CANNIBALISM. 



Even though there are differences in the early extra-ovarian 

 histories of the food products, the consumption of eggs and em- 

 bryos by the developing larvae of Fasciolaria is fundamentally 

 similar to those other cases among gastropods in which certain 

 young are used as food after being broken down, or are preyed 

 upon directly by their competitors. It seems to me justifiable, 

 therefore, to include all these methods of nutrition, based on the 

 consumption of materials derived from the ovary of the mother, 

 but not contained within the eggs from which the consumers 

 come, under one term, cannibalism. The various degrees to 

 which cannibalism is developed in different gastropods have been 

 arranged in series by earlier writers, and though this series is both 

 interes'ting and instructive it has no phylogenetic significance, 

 and I shall try to show that the phenomenon in Fasciolaria can 

 be explained independently. 



McMurrich ('85) noticed that some of the " ova" in the capsules 

 of Crcpidula fornicata, C. plana and C. convexa break down and 

 are used as food by the survivors, although this process is not so 

 pronounced as in Purpura floridana. Koren and Danielssen 

 ('57) described the case of Bnccinnni nndatwn which is very sim- 

 ilar to that of Fasciolaria in the disproportion between the num- 

 ber of embryos developing in the capsules and the number of 

 eggs furnished by the female, Buccinum, however, differs from 

 Fasciolaria because many of the ova, which do not form embryos, 

 divide. Carpenter in the same year ('57) corrected the view of 

 Koren and Danielssen that the embryos originate by conglomer- 

 ation, by describing the development of Purpura lapillus in 



