GASTEROPODES. 279 



two circular spots, very perceptible,, possibly the site of originating corni- 

 cula : also a spine or other organ projecting in front of the Nautiline. 

 Plate XXXVIII. fig. 15. All these animals at length disappeared after 

 the wonted contraction, leaving their numerous shells below. 



It is singular we should never behold any similitude to the parent 

 in any of the animals quitting the spawn. Some have very freely called 

 them the larvas, that is, they are presumed to be the larvae, or an em- 

 bryonic form, which shall undergo certain metamorphosis in its growth, 

 until in maturity it shall resemble the parent. But I have not under- 

 stood that any observer has hitherto witnessed its progress. In another 

 work I have shewn the like obstacles in opposing our discovery of the 

 the advances of young animals which pass through similar changes. 



There is little doubt, if we may reason from analogy, that in the 

 Nautiline we behold only the prelude to metamorphosis. 



The Doris and the Limax are closely allied, therefore I may be per- 

 haps allowed to compare the species now under discussion, the largest of 

 the tribe, with the largest of the Scotish testaceous univalves, the Murex 

 antiquus, which is occupied by a Limax. 



This animal spawns profusely in the month of April and later. The 

 spawn is of very peculiar formation, consisting of a number of capsules 

 in adhesion, sometimes forming a mass larger than the whole animal. 

 Each capsule is nearly a spherical segment, containing from ten to twenty 

 embryos ; but these are not individually contained in integuments in- 

 vesting them singly, which would retain the embryo in its place. 

 Plate XXXIX. fig. 3. The embryo within the capsule, which is yellow, 

 becomes gradually more conspicuous, as with the Doris, each grows 

 more distinct. When hatched, it consists of a shell of a single volute, 

 with a wide orifice, fig. 4, containing an animal, whose margin is pro- 

 longed as if in a double scoop, which is bordered by active cilia. Their 

 rapid motion produces a vortex, attracting minute buoyant particles in 

 the water. A distinct view of all the intemal structure is observed by 

 the opacity of the parts. But behind this organization a little farther 

 down, the pulsation of a vessel, perfectly transparent, is perceptible. 

 Plate XXXIX. figs. 5, 6. The whole subject does not exceed half a line 



