OOTHEC.E OF NASSA AND OF NATICA. 503 



in a strong horny outer coat, but slit along the upper 

 edge, so as readily to allow the exit of the little 

 whelklings when mature. 



Nassa reticulata, another form of Whelk, deposits 

 its egg-capsules on weeds or stones fastened together, 

 and overlying each other like the brass scales on 

 the cheek-band of a soldier's helmet, each capsule 

 having a shape like that of the spade on playing-cards. 

 They consist individually of compressed pouches, 

 nearly of the size of a silver penny, supported on very 

 short pedicles, and opening at the top to give a door- 

 way to the embryo when sufficiently advanced in 

 growth. 



The ootheca of Natica are extremely curious, and 

 were formerly described as a zoophyte, under the name 

 of Flustra arenosa. The parent mollusk in this case 

 either leaves its egg-clusters loose in sandy places, or 

 attaches them so carelessly, that they frequently be- 

 come loose ; and the object of the remarkable form of 

 the gristle-like mass under which they present them- 

 selves would seem to be to fit it for lying on sand 

 without becoming deeply imbedded in it. 



The shape of this substance is remarkable ; it greatly 

 resembles the hoof of a colt, and is about equal in 

 thickness to the peel of an orange. It is composed 

 of fine particles of sand, cemented by an animal 

 gluten, very friable when dry, in which condition it 

 bears a striking resemblance to a piece of Scotch oat- 

 cake. If held to the light it appears full of cells, 

 arranged nearly in quincunx order, that, in fact, are 

 so many capsules wherein the ova are contained ; and 

 these, if kept in the aquarium until they are hatched, 



