^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 Grasteropoda. With the Apneusta, and the 

 Heterobranchia, the two lobules produced by the indentation just indi- 

 cated, 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 the interior. 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. ''^' At the same time, also, the naked 

 Grasteropoda lose their shell and operculum. 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- bo, Nerita, Buccinum, and Purpura. Judging 

 terobranchia owes its progress principally to the from Cams'' figure (Nov. Act. Acad. Nat. Cur. 

 following works : Sars, in JViegmaiiii's Arch. 1837, XIII. 1827, p. 767, Tab. XXXIV. fig. 2) of the 

 I. p. 402; 18-10, I. p. 196, Taf. V.-VH. 18-15, I. p. embryo of Paludina vivipara, it also has at this 

 4, Taf. I. fig. 7-11 (Tritonia, Doris, Aplysia, and age a puiiou. 



Aeolis) ; Loven, in the Kongl. Vetensli. Akad. This remark is also applicable to the young animals 

 Handl. 1839, p. 227, or Isis, 1842, p. 360, Taf. I. found by Lund (Ann. d. So. Nat. I. 1834, PI. VI. 

 (Aeolis); Van Beneden, Ann. d. Sc. Nat. XV. fig. 9-14) in the egg-capsules of a Jl/urei' (?) and a 

 1841, p. 123, PI. I. {Aplysia) ; Nord?mmn, \oc. cit. Natica{?). I have found, in the pyriform oviger- 

 p. 71, Taf. IV. V. {Tergipes) ; Allman, loc. cit. ous capsules adhering to the orifice of the shell of 

 p. 152, PI. VII. fig. 10-12 ; Vost, Compt. Rend. Vermetus, young with highly-developed pinions 

 XXI. 1845, No. 14, XXII. No. 9, or Froriep''s having long cilia, and with a regularly convoluted 

 neue Not. No. 795, 820 (Jciaf on) ; and Rejfi, Ann. shell, such as has been described by Philippi 

 of Nat. Hist. XVII. 1846, p. 377, PI. X. {Doris and {lViegmann''s Arch. 18-39, I. p. 128, Taf. IV. fig. 

 Polycera). Vogt has since published his entire 8). Loven has observed similar emlwyos swim- 

 Memoir on the development of Actaeon viridis in ming with two pinions, with the Ilet^-robranchia 

 the Ann. d. Sc. Nat. VI. 1846, p. 5, PI. I.-IV. ; see of the genera Elysia, Bulla, Bu/laea, and with the 

 also Schleiden, and Froriep''s Not. II. p. 77, fig. Peotinibranchia of the genera, Lacuna, Cerithium, 

 1-12. and Eulima ; see Arch. Skandinav. Beitr. &c. I. 



3 These remains of the two pinions are easily seen 1845, p. 154, Taf. I. fig. 1-8. 



with Tergipes, Aeolis, Doris, Tritonia, Aplysia, 5 The development of the Pulmonata which have 



and other Heterobranchia. The ciliated lobes on the a shell, has often fi.xed the attention of naturalists, 



head of Thetis, are only these pinions persisting in See Stiebel, loc. cit. p. 38, Tab. II. and in Meck- 



an eral)ryonic form ; see Loven, loc. cit. eVs Arch, deutsch. I. p. 423, II. p. 557, Taf. VI. ; 



■1 According to Loven (loc. cit. or Isis, 1842, p. Hugi, Isis, 1823, p. 213 ; Cams, Von den iiusseren 



306, Taf. I. fig. 22), the young of Rissoa have a Lebensbed. loc. cit. p. 60, Taf. I. ; Prevost, Ann. 



very large pinion. Nordmann (loc. cit. p. 98) has d. Sc. Nat. XXX. 1833, p. 40 {Lymnaeus) ; Pfeif- 



confirmed this, and found an analogous one with fer, Naturg. deutsch. Land-und Siisswasser-Mol- 



Littorina, iind Phasianella. The small MoUusks lusk. Abth. III. p. 70, Taf. I. (Helix); Quatre- 



with a pinion and a turbinated shell, of which Sars fages, Ann. d. Sc. Nat. II. 1834, i). 107, PI. XI. 



(Beski-ivel. loc. cit. p. 77, fig. 38, 39) has formed the B. (Lymnaeus and Planorbis) , Jacquemin, Ibid, 



genus Cirropteron, have since been found by him- V. 1836, p. 117, 119, and in the Nov. Act. Acad, 



self, to be young individuals of Turbo, Trochus, &c. XVIII. 1838, p. 636, Tab. XLIX. L. (Planor- 



or Nerita.; this accords with Granfs observations bis) ; Dumortier, Nouv. Mtm. de I'Ac'ad. Roy. de 



fEdinb. new PhUos. Jour. No. 13, 1827) upon Tur- BruxeUes, X. 1837, PI. I.-IV. and Ann. d. Sc. Nat. 



23 



