GASTEROPODKES. 271 
the neck, of more complex structure ; besides, in certain species, long 
prolongations of the shoulder, apparently exercising a tentacular faculty : 
and a number of branchie, Variously disposed in external arrangement. All 
individuals are distinguished by extraordinary fertility. Much diversity, 
according to genera and species, distinguishes the spawn ; and the young 
of all apparently undergo a remarkable metamorphosis, in their progress 
to maturity. 
On minute investigation, I believe, a correspondence may be found 
between the form of the head, the structure and arrangement of the 
branchixw, and the mode wherein the spawn is deposited. 
Section I. Trrronia.—Body solid, invested by a cloak. Tentacula 
two, retractile, within sockets. Branchiz marginal, erect, palmate. 
1. TrrrontA Hompercu—Homberg’s Doris.—Plate XX XVIII. 
This is the giant of the race, insomuch that the naturalist, familiar 
with the puny specimens of ordinary occurrence, can hardly persuade 
himself, on seeing them together, that they belong to the same genus. 
He deems its association, even with the best of the larger kind, as some- 
what incongruous, the mass is so unwieldy. 
But the vast disproportion between the parts of kindred animated 
beings, while the vital functions are alike effective in both, is well adapted 
to prove the excellence of the model whereon they are framed. 
The rarity of adults having attained their full dimensions in the 
Scotish seas, my ignorance of the quality of their food, the difficulty of 
preservation, and the injuries of atmospheric influence, for a long time 
embarrassed my exertions to ascertain any definite points in the history 
of this remarkable species. Nor, in this country, will it be easy for any 
one to counteract these obstacles, or to find a remedy. 
But we have, further, to conjoin the sluggish disposition of all the 
tribe, doubtless extending to their native haunts ; and the exhaustion, 
almost to the death, inseparable from the waste, concomitant on spawn- 
