242 MR. J. D. MACDONALD ON THE PROBABLE METAMORPHOSIS 



teeth of Eanella or Dolitmi, with the spherical otolithes common to all ; and it is highly 

 probable that it will ultimately prove to be the young of some neighbouring genus. The 

 little shell itself is perfectly identical with the summit of the sjiii'e of a species of Malea 

 which is very common in the South Seas. I regret much that I have not yet had an 

 opportunity of examining the animal of the latter for the purpose of more accurate 

 comparison ; but this much I can say — that the lingual teeth of Dolium, which cannot be 

 far removed from Malea, very closely resemble those of Macgillivraia. 



I formerly figured and described a pelagic Gasteropod with six ciliated arms, and which 

 I believe may be safely referred to the Tritonidce. I now offer the portrait of another 

 species, obviously belonging to the same genus, though occupying a very differently 

 shaped shell. In the paper alluded to I also noticed a minute Natica, with mentum, 

 lateral labial plates, septiserial tongue-strap, and, in fact, only differing from other or at 

 least full-grown members of the genus in the possession of a cervical circlet of ciliated 

 arms, and a vesicular float ; but I am now quite satisfied that I have identified this 

 species with the nucleus of a handsomely spotted Natica occurring in deep water. 



It is very remarkable that the characteristics just mentioned should be present in all 

 the little pelagic Gasteropoda, while their internal anatomy unmistakeably refers them to 

 very different families. But if, in connexion with these particulars, we take into con- 

 sideration the large size of the fatty globules contained hi the sacculi of the liver, indica- 

 tive of almost incipient development, and the total absence of ova or spermatozoa (at 

 least so far as the matter has yet been investigated), it can scarcely be doubted that these 

 little creatures are not perfect, but transitional forms, the further development of whose 

 head and proboscis, coincident with the shedding of the ciUated arms and a general adap- 

 tation to a new sphere of existence, may, with all propriety, be regarded as a veritable 

 metamorphosis. It also appears to me that a bold indication of a developmental change 

 such as this, is exhibited in the abrupt transition from the marking of the young shells 

 into the very different and characteristic sculptm-ing of the adult state of the corresponding 

 species, — an occurrence which takes place long subsequent to the period at which, in 

 some instances, a sinistral nucleus merges into a dextral shell. 



Since the above remarks were written, as if to afford them additional support, a suc- 

 cessful haul of the towing-net has made me acquainted with another little genus, of which 

 I had no previous knowledge. It was invested vrith a thick and globose cartUaguious 

 envelope, with an irregular subterminal aperture, not very unlike that of the cartila- 

 ginous covering of tlie Pteropod Euryhia. 



On endeavouring to remove the animal from this singular shell, I found that it was 

 indeed but an external case, probably the egg-capsule itself; for the little creature very 

 readily came away occupying the true shell, which was yet so membranous and delicate 

 as to become folded by pressure, without fracture. The necessity of a fm-ther protection to 

 the tiny occupant, cast abroad iipon the ocean of life, will be at once apparent on in- 

 specting the figure. The tentacula were of considerable length, with oceUi at their bases ; 

 and the mouth was encircled by a deeply cleft calyx of fom- segments, with richly ciliated 

 margins. The foot much resembled that of Atlanta, minus the swimming plate, and 

 presented a very distinct though rudimentary creeping disc and a broad three-lobed 



