280 GASTEKOPODES. 



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 branchise were denoted by a few tubercular prominences, and 

 the formation of the head was almost alike indefinite. Plate XXXVIII. 

 fig. 9 ; fig. 10, the same, enlarged. 



In specimens of inferior dimensions the branchiae 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 branchiae, 

 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 



