1007.] NATURAL SCIEXCES OF PHILADELPHIA. 321 



of the normal dcvclopinent of large and of small eggs might be expected 

 to shed some light. Undoubtedly experiments, if they could be suc- 

 cessfully performed, would be of great value in answering these ques- 

 tions, but in the case of the gasteropods which I have studied I have 

 not found it possible to test these questions experimentally. 



The development of gasteropods is extraordinarily varied in respect 

 to the manner of nourishing the embryo and larva. In some cases, 

 and these pi-csumably the more primitive, the eggs are small and con- 

 tain little yolk and the free swimming larva) (veligers) are set free at 

 an early age to shift for themselves {e.g., Crepidula plana, Patella, 

 Acma:a, etc.). In others the eggs contain a larger quantity of yolk 

 and the free-swimming life is correspondingly reduced {e.g., Crepidula 

 jornicata, Illyonassa, etc.). In still others the eggs contain a yet 

 greater quantity of yolk and the veliger stage is passed entirely within 

 the egg capsules, the young escaping in practically an adult condition 

 {e.g., Crepidula convexa and adunca, Urosalpinx, Sycotypus, Fid gur, etc.). 



A most curious and interesting method by which nutriment is 

 supplied to the embryo is found in those gasteropods in which a large 

 number of relatively small eggs is laid, only a few of which develop, 

 the others being eaten as food by the developing embryos {e.g.. Purpura, 

 Buccinum, Fasciolaria, Neritina, etc.). 



For the purposes of the present study the only instances which we 

 shall consider are those in which the food for the developing embryos 

 is contained within the egg in the form of j^olk. The early develop- 

 ment of a considerable number of gasteropods is now well known, but 

 most of these belong to that group having relatively small eggs. It 

 has seemed to me worth while to compare with these the development 

 of the largest gasteropod egg of which I have any knowledge, viz., that 

 of Fulgur carica. The eggs of this species are about one-sixteenth of 

 an inch in diameter; those of a closely allied form, Sycotypus canalli- 

 culaius, are about one-twenty-fifth of an inch in diameter. The eggs 

 of Fulgur are about thirteen times the diameter and about 2,200 times 

 the volume of the eggs of Crepidula plana, with which I shall par- 

 ticularly compare them. I have also studied several other species 

 in which the eggs are intermediate in size between these two extremes, 

 as shown by the following table: 



Fulgur carica, 1,700 //in diameter. 



Sycotypus canalliculatus, 1,000 /jl " 



Crepidula adunca. . : 410 ij. " 



" convexa, 280 ,« " 



" fornicata 182 /« " 



plana, 136 ,« " 



