158 O. C. GLASER. 



p. 409) the non-fertilization of the majority of the ova, whereby 

 it is impossible for them to develop to any great extent, and 

 whereby they naturally break down when they have endeavored 

 to segment. We see this in Neritina, Buccinuui and Pnrpnra 

 lapillns. In Fasciolaria, as stated above, the process reaches its 

 climax, and in this case the sterile, nutritive ova do not show the 

 least trace of segmentation, nor do they ever show signs of ma- 

 turation." 



This second factor seems to me most important, and in view 

 of recent results on the development of the germ cells of gas- 

 tropods, places the origin of cannibalism in a new light. In 

 the first place the ingested materials may consist of undivided 

 eggs, or of embryos or of a combination of these classes of 

 constituents. Thus in Ncritina and Fasciolaria the ingested 

 eggs do not divide. In Buccimtin most of the ingested ova 

 divide, though some do not, and in Crepidula, Pnrpnra and 

 Urosalpin.v, the ingested materials are derivatives of either early 

 or late stages of development. The habit of Fasciolaria, though 

 coming in the class with that of Neritina, also resembles that of 

 Crcpidula, Pnrpnra and Urosalpin.v, for the abnormal larvae of 

 the pre-cannibal period, as well as many of the abnormal late 

 ones, including some dwarf larvae, are ingested together with the 

 unfertilized eggs. That these materials are taken in by the 

 embryos requires no explanation in this connection, for not 

 only are they obviously useful as food, but the structures in 

 virtue of which the larvae cannot help ingesting all the available 

 substances in their environment were evolved, for locomotion and 

 for swallowing other things, in all probability long before Fascio- 

 laria exchanged its pelagic larval life for the safer one within 

 capsules. To explain the origin of the habit of cannibalism it 

 seems to me necessary to answer only two questions : (i) Why 

 do some of the embryos break down ? (2) Why are many 

 of the eggs infertile ? By answering these questions materials 

 to be swallowed are accounted for : the consumers, and the 

 mechanism by which the consumption is brought about, are the 

 results of that portion of the phylogenetic history of Fascio'.aria 

 which preceded the origin of cannibalism. Given therefore 

 ingestors, and materials to ingest, cannibalism follows as a natural 

 consequence, needing no further explanation. 



