280 GASTEROPODES. 
in length ; the animal has a very solid aspect, and vivid yellow colour, 
which is chiefly derived from minute ovoidal pellets occupying the 
stomach, which are profusely discharged. 
The correspondence of the nascent Murex with the Nautiline, is such 
as to sanction the conclusion that the latter is actually the progeny of 
the Doris, though we find preservation throughout its metamorphosis 
impossible. 
But certain evident changes are seen in the ova of the Tritonia, 
although the earliest may not have been observed, because the animal 
cannot be then procured or preserved. With scanty organization a gra- 
dual accession of parts and new segments ensue, as with many creatures 
of the lower orders. In a young specimen, not above two lines long, the 
originating branchiz were denoted by a few tubercular prominences, and 
the formation of the head was almost alike indefinite—Plate XX XVIII. 
fig. 9 ; fig. 10, the same, enlarged. 
In specimens of inferior dimensions the branchiz are few, and of 
greater simplicity than in adults. At that time, or rather on an increase 
of their number by the animal advancing, they seem to be arranged in a 
double row on each side of the cloak, one being within the line of the 
other ; and the whole border composed of them consisting of those alter- 
nately larger and smaller. Thus, supposing the first of the branchie, 
next the corniculum, to be larger, and in the outer line, the next of the 
inner line is smaller. If the first of the outer line be small, the next of 
the inner is large. In later stages their structure is more pinnate ; they 
are light and feathery, whereas in the earlier stages, they are somewhat 
foliaceous or palmate. 
All these characters are stronger or weaker according to the speci- 
mens ; and very often according to their degree of development from pre- 
valent temperature or other cause. 
Specimens are very impatient of heat ; they require copious and fre- 
quent renewal of their element. 
A great quantity of mucus is secreted from the skin, possibly de- 
signed by Nature only for temporary purposes. Brushing it off with a 
feather seems beneficial. The secretions are very ample from the tribe 
