242 MR. J. D. MACDONALD ON THE PROBABLE METAMORPHOSIS 
teeth of Ranella or Dolium, 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 spire 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 Doliwm, 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 Tritomidæ. 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 in 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 ciliated 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 characteristie sculpturing 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 with a thick and globose cartilaginous 
envelope, with an irregular subterminal aperture, not very unlike that of the cartila- 
gious covering of the Pteropod Burybia. 
| On endeavouring to remove the animal from this singular shell, I found that it was 
xm bes eiii ug ca, probably the egg-capsule itself; for the little creature A 
CINE: se : cupying the true shell, which was yet so membranous and nn 
the tiny occupant ni ee ficte ui Å 
HARAS : à SEREN upon the ocean of life, will be at once apparent on = 
OP Rea "ws rx. Ha entacula were of considerable length, with ocelli at their oiam 
„~ mouth was encircled by a deeply cleft calyx of four segments, with richly ciliated 
a — — that of Atlanta, minus the swimming plate, " 
ough rudimentary creeping dise and a broad three-lo 
