$ 229. THE CEPHALOPHORA. 265 
a delicate ciliated epithelium. By the means of these cilia, the embryo 
rotates upon its axis for a long time. From this period, the aquatic differ 
widely from the pulmonate Gasteropoda. With the Apneusta, and the 
Heterobranchia, the two lobules produced by the indentation just indi- 
ated, enlarge and change into round pinions (Vela), upon whose borders 
very long cilia are gradually developed. A third eminence is developed 
between these two pinions, and, ultimately, changed into the foot. 
Although the ciliated epithelium is always most widely spread around 
‘these two pinions, which should be regarded as situated on the anterior 
extremity of the body, yet there is formed a thin shell upon the posterior 
extremity of the embryo, whether this last belongs to a conchiferous 
‘species or not. At the same time, there appears upon the dorsal part of 
the foot, an operculum corresponding as to size with the opening of the shell. 
Among the internal organs, the two auditive capsules appear first; and 
when these have become quite distinct, the eyes are seen. Following these, 
are developed the.tentacles, the border of the mantle, and the mouth which 
appears between the two pinions. At the same time. the stomach, the 
intestine, and the liver, individually appear in theinterior. At this epoch, 
the young leave the egg and swim freely about by means of the long cilia 
which are situated on their extended and rigid pinions.” Subsequently 
‘these pinions disappear, or are changed into two tentacular prominences 
situated on each side of the mouth.® 
4Gasteropoda lose their shell and operculum: 
At the same time, also, the naked 
From the isolated facts hith- 
erto published upon the embryology of other branchiferous Gasteropoda, it 
may be concluded that they experience a similar metamorphosis, only the 
shell of the embryo, at this time, usually presents some convolutions. 
In the development of the operculate Pulmonata, there is no analogous 
metamorphosis.” The embryo lengthens a little when it begins to rotate 
2 The embryology of the Apneusta, and the He- 
iterobranchia owes its progress principally to the 
following works : Sars, in Wiegmann’s Arch. 1837, 
I. p. 402; 1840, I. p. 196, Taf. V.-VII. 1845, I. p. 
A, Taf. I. fig, 7-11 (T'ritonia, Doris, Aplysia, and 
Aeolis); Lovén, in the Kong]. Vetensk. Akad. 
andl. 1839, p. 227, or Isis, 1842, p. 360, Taf. I. 
(Aeolis); Van Beneden, Ann. d. Se. Nat. XV. 
1841, p. 123, Pl. I. (Aplysia) ; Nordmann, loc. cit. 
p. 71, Taf. IV. V. (Tergipes) ; Allman, loc. cit. 
‘p. 152, Pl. VIL. fig. 10-12; Vogt, Compt. Rend. 
X XI. 1845, No. 14, XXII. No. 9, or Froriep’s 
meue Not. No. 795, 820 (Actaeon) ; and Reid, Ann. 
of Nat. Hist, XVII. 1846, p. 377, Pl. X. (Doris and 
Polycera). Vogt has since published his entire 
Memoir on the dev of Actaeon viridis in 
the Ann. d. Sc. Nat. VI. 1846, p. 5, Pl. I-IV. ; see 
also Schleiden, and Froriep’s Not. Il. p. 77, fig. 
1-12. 
8 These remains of the two pinions are easily seen 
with Tergipes, Aeolis, Doris, Tritonia, Aplysia, 
and other Heterobranchia. The ciliated lobes on the 
head of Thetis, are only these pinions persisting in 
an embryonic form ; see Lovén, loc. cit. 
4 Acccrding to Loven (loc. cit. or Isis, 1842, p 
366, Taf. I. fig. 22), the young of Rissoa have a 
very large pinion. MVordmann (loc. cit. p. 98) has 
confirmed this, and found an analogous one with 
Littorina, and Phasianella. The small Mollusks 
with a pinion and a turbinated shell, of which Sars 
(Beskrivel. loc. cit. p. 77, fig. 38, 39) has formed the 
genus Cirropteron, have since been found by him- 
self, to be young individuals of Turbo, Trochus, 
or Nerita; this accords with Grant’s observations 
Edinb. new Philos. Jour. No. oe upon T'ur- 
& 
bo, Nerita, Buccinum, and Purpura. Judging 
from Carus’ figure (Nov. Act. Acad. Nat. Cur. 
XIII. 1827, p. 767, Tab. XXXIV. fig. 2) of the 
embryo of Paludina vivipara, it also has at this 
age a pinion. 
This remark is also applicable to the young animals 
found by Lund (Ann. d. Sc. Nat. I. 1834, Pl. VI. 
fig. 9-14) in the egg-capsules of a Murex (?) anda 
Natica(?). Ihave found, in the pyriform oviger- 
ous capsules adhering to the orifice of the shell of 
Vermetus, young with highly-developed pinions 
having long cilia, and with a regularly convoluted 
shell, such as has been described by Philippi 
(Wiegmann’s Arch. 1839, I. p. 128, Taf. IV. fig. 
8). Loven has observed similar embryos swim- 
ming with two pinions, with the Heterobranchia 
of the genera Elysia, Bulla, Bullaea, and with the 
Pectinibranchia of the genera Lacuna, Cerithium, 
and Eulima; see Arch. Skandinav. Beitr. &c. I. 
1845, p. 154, Taf. I. fig. 1-8. 
5 ‘The development of the Pulmonata which have 
a shell, has often fixed the attention of naturalists. 
See Stzebed, loc. cit. p. 38, Tab. II. and in Meck- 
el’s Arch. deutsch. I. p. 423, II. p. 557, Taf. VI. 3 
Hugi, Isis, 1823, p. 213 ; Carus, Von den ausseren 
Lebensbed. loc. vit. p. 60, Taf. I. ; Prevost, Ann. 
d, Sc. Nat. XXX. 1833, p40 (Lymnaeus) ; Pfeif 
Jer, Naturg. deutsch. Land-und Stisswasser-Mol- 
lusk. Abth. III. p. 70, Taf. I. (Helix); Quatre- 
Jfages, Ann. d. sc. Nat. II. 1834, p. 107, Pl. XT. 
B. (Lymnaeus and Planorbis) , Jacquemin, Ibid. 
V. 1836, p. 117, 119, and in the Nov. Act. Acad. 
&c. XVIII. 1838, p. 636, Tab. XLIX. L. (Planor- 
bis) ; Dumortier, Nouv. Mém. de l’Acad. Roy. de 
Bruxelles, X. 1837, Pl. I.-IV. and Ann. d. Sc. Nat. 
