DORIS. 



foot (figs. We, 12 e) — is observed to develop itself a little behind them on the median line. A 

 shell (figs, lie, 12c) closely investing the inferior portion of the embryo, the lobes and 

 rudimentary foot being uppermost. The shell rapidly increases, and assumes a nautiloid 

 form ; afterwards the foot displays, attached to its posterior surface, a circular operculum 

 (fig. 13 d), which is opposed to the mouth of the shell. The lobes (fig. 15/) now expand into 

 two large, flattened, ovate appendages, with very long vibratile cilia around the margins, and 

 the larvae are at length mature. The whole mass of spawn now presents the utmost animation; 

 hundreds of these busy atoms are seen, each within its transparent membranous cell, rotating 

 with great agility and ceaseless perseverance, the cilia all the while vigorously vibrating on 

 the margins of the outstretched lobes. The membranous chorion, which by this time has 

 become enlarged, ultimately gives way, no longer able to resist the perpetual struggle within, 

 and the liberated larva, wending its way through the shattered shreds of the general envelope, 

 boldly trusts itself to the open, trackless waters, where, doubtless, thousands and tens of 

 thousands perish ere they find a fitting resting place ; some being swept away by resistless 

 currents, others falling a prey to ever watchful and innumerable enemies. 



On close examination, the shell of the larva is found to be of excessive delicacy, exquisitely 

 brilliant, and so transparent that its exact form is not very easily made out. In all the species 

 it is of a nautiloid character, with the spire of scarcely one volution, and invariably a little 

 twisted to one side. It is, in fact, the commencement of the ordinary testaceous covering of 

 a gasteropod, and were its growth continued, it would assume the usual spiral form. In 

 D. tuberculata the shell is rather shallow, while, in some of the JEolididce (Fam. 3, PL 1, 

 figs. 5, 6), it is of considerable depth; and in Uolis olivacea, it (fig. 9) may be said to be 

 altogether without a spire. Weak acetic acid destroys the shell ; but the operculum remains 

 unaffected by it. There can be little doubt, therefore, that the former is calcareous, and the 

 latter horny.* 



The larva is somewhat opaque, and is enveloped in a very wide, thin, delicate, and trans- 

 parent membrane or cloak (PI. 3, fig. 15m), which partially lines the shell, being in contact 

 with it at the mouth, and at the bottom where the retractor muscle (n) is attached to it. This 

 is a strong band, with the end in contact with the shell, a little enlarged ; it passes upwards, 

 and is lost in the midst of the larva, which, in D. tuberculata, is so opaque that the various 

 parts are not easily determined. In Uolis coronata, however, they can be readily distinguished. 

 In this species, as well as in Doris tuberculata, Doto coronata, and Eolis picta, the ciliated oral 

 lobes are large; but they are small in K olivacea (Fam. 3, PI. 1, fig. 9), Herniaa dendritica 

 (Fam. 3, PI. 40, fig. 7), and Polycera quadrilweata (Fam. 1, PI. 22, fig. 11). The mouth 

 (Fam. 1, PI. 3, fig. 15/) is situated between and a little behind these lobes, and is a mere 

 circular opening of considerable dimensions : the oesophagus passes downwards from this 

 opening, and is a rather wide and straight tube, which, suddenly swelling out, is formed into 

 a rounded, in some species an elongated, pyriform, well-marked stomach (h). The intestine (i) 

 is considerably constricted, and leaves the stomach at the extremity opposite to the cardiac 



* The same is the case with the larva of Aplysia : on placing it in weak acetic acid, air bubbles 

 were immediately formed, and on account of their rapid generation, the shells were jerked about. In 

 a short time these latter entirely disappeared, leaving exposed the animal enveloped in its cloak. The 

 operculum was not in the least changed. 



