322 PROCEEDINGS OF THE ACADEMY OF [Jl^l^Y; 



The great difference in the sizes of these eggs is not due to a pro- 

 portionate difference in all their constituents, viz., protoplasm as 

 well as yolk, but almost entirely to the varying amovmts of 3^olk which 

 they contain, and this fact suggests the possibility of examining the 

 influence of yolk upon development by comparing the development 

 of one of the largest gasteropod eggs with one of the smallest. 



A paper on the embryology of Fulgur was published by McMurrich 

 (1886) more than twenty years ago. This paper deals in a general 

 way with the development of this genus, questions of cell lineage and 

 egg organization being at that time almost unknown. Further refer- 

 ence to McMurrich's work will be made throughout the course of this 

 paper. A subsequent paper by the same author (1896) deals with the 

 yolk lobe and centrosome of Fulgur. Some features in the develop- 

 ment of this form were also considered by me (1897) in a paper dealing 

 more particularly with Crcpidula. Other than this the development 

 of Fulgur has not been made the subject of any detailed study. 



2. BREEDING HABITS. 



For the sake of completeness I shall here mention some observa- 

 tions on the breeding habits of Fulgur and Sycotypus. In both of 

 these forms the eggs are laid in peculiar disk-shaped or lenticular 

 capsules w-hich are attached in a series along a central cord. With 

 the exception of the first few capsules formed, wliich are small and 

 usually contain no eggs, each capsule contains from ten to twenty 

 eggs embedded in a gelatinous substance which fills the capsules. 



The method of forming the peculiar string of capsules characteristic 

 of these genera is sufficiently interesting to merit a brief description. 

 During the process of egg-laying, the foot of the female is contracted 

 and partially withdrawn within the shell. A mucous-like secretion 

 is then poured out from the nidamental organ through the folds of the 

 partially contracted foot, and this secretion is applied to some solid 

 object to which it adheres, or it is merely buried in the sand. In the 

 case of Fulgur this first formed portion of the "string" is liiu'ied deeply 

 in the sand ; in certain specimens of Sycotypus which 1 kept in a wooden 

 car, or float, the egg string was attached to the boards of the car. The 

 first formed capsules on the string are small, far apart and contain no 

 eggs. Later formed capsules increase in size and in the number of 

 eggs contained in each, and successive caijsulcs lie closer together on 

 the string. During the process of laying the female is cjuiescent, and 

 is usually bmied beneath the surface of the sand, only the siphon 

 protruding. The eggs, surroimded by the albimien and the secretion 



