26 THE UNIVERSITY OF OKLAHOMA 



XIII. THE EGG LAYING HABITS OF HAMINEA 



VIRESCENS (SBY) 



A. Richards. 



From the Zoology Laboratory of the University of Oklahoma. 

 Contribution No. 15 Second Series. 



During the summer of 1921 the writer studied the effect of a 

 number of accelerants upon the cleavage of the eggs of the opistho- 

 branch Hamiiica vircscciis (Sowerby) at the laboratory of the 

 Scripps Institution for Biological Research at La Jolla California. 

 The eggs of this animal are particularly favorable for experiments 

 in which it is desired to test the effect of some special factor while 

 leaving the egg in an environment that is normal in all respects ex- 

 cept that investigated. The animals were, brought into the laboratory 

 and kept in a dish of running sea water supplied with a quantity 

 of stones and sand from the tidal flat where they were first 

 secured. Although they would at length become exhausted no diffi- 

 culty was experienced for some days in getting them to produce 

 eggs. 



The manner in which the eggs are laid in Haminca virescens 

 differs from the only descriptions which the writer has seen re- 

 corded. The most definite accounts deal with Haminea solitaria, 

 however, and it may be that in that form the eggs are fastened as 

 described to the rocks as masses of jelly, or are attached by stalks 

 to the sand. The eggs of Haminca virescens as deposited in the 

 laboratory certainly do not answer this description. 



The eggs are laid in a jelly mass which has the appearance of 

 a short piece of narrow but very thick ribbon. It is of rather com- 

 plicated structure. The eggs appear to be extruded in a string of 

 tough gelatinous material. The string itself is laid in a zigzag 

 fashion so that the appearance is that of a double row of eggs. It 

 is, however, accurately placed in the form of a flattened spiral 

 for the loops are not formed by simple back and forth folds, as 

 they at first appear; but are so arranged that the loops are com- 

 pressed against each other. This produces the effect of a thick 

 cross sriated ribbon. The structure of the egg mass is illustrated on 

 Plate II, page 38. In one typical ribbon, 242 loops were counted, 

 in each of which the eggs averaged 90; this gave a total of 21,780 

 eggs for this ribbon. Probably 20,000 is an average number for a 

 ribbon produced under typical conditions. 



In each ribbon the eggs are uniformly all in the same stage of 

 development, indeed in the same stage of mitotic division. It is 

 a remarkable fact that 20,000 eggs should be dosposited in as com- 

 plicated a manner as these, and all be in the same stage of division. 



