GASTROPODA ANfSOPLEURA. 483 



forwards as in Azygobranchia, may become median and posterior ; left ctenidium 

 and right nephridium only retained (see p. 479, and note) ; ctenidium and mantle- 

 fold sometimes lost. Hermaphrodite. 



(i) Opisthobranchia. Visceral dome always small ; shell rarely present ; a nauti- 

 loid shell in the Veliger stage. Foot large in archaic forms, and mantle-fold projecting 

 over right side. Anus then placed far back beyond mantle-edge, behind the cteni- 

 dium, the free end of which is turned backwards. Heart in front of base of 

 ctenidium. Epipodia commonly present and often reflected over shell or dorsal 

 surface. Marine. 



(a) Palliata (= Tectibranchia). Mantle-fold present. Includes (i) Ctenidiobran- 

 chia, a ctenidium present; shell, with rare exceptions, delicate, sometimes small 

 or completely enclosed within the reflected mantle-edge ; epipodia common, e. g. 

 Bulla^ Aplysia, P leurobranchus : (ii) Phyllidiobranchia, ctenidium atrophied, re- 

 placed by a lateral row of lamellae on each side within the pallial fold, e. g. 

 Phyllidia. 



(/3) Non-Palliata ( = Dermatobranchia). Mantle atrophied in adult ; and shell 

 lost ; body slug-like, visceral dome and foot co-extensive ; anus usually median 

 and posterior. Includes (i) Pygobranchia, ctenidium (?) a circlet of pinnate processes 

 round the anus; epipodial-fold may be large and simulate a mantle-fold; cerata 

 sometimes present, e. g. Doris ; Polycera\ (ii) Ceratonota, ctenidium aborted; simple 

 or branched cerata, into which liver processes usually pass ; anus on right side, or 

 dorsal and median: e. g. Tethys, Eolis ; (iii) Haplomorpha, no ctenidium; no cerata; 

 foot also sometimes lost ; degenerate and small, e. g. Phyllirhoe, Elysia. 



(2) Pulmonata. Ctenidium aborted; dorsal wall of branchial cavity formed 

 by mantle, respiratory ; osphradium on left side (Planorbis, Auricula) or right 

 (Limnaeus}; usually lost; visceral dome small and co-extensive . with foot, e.g. 

 Limax, Arion, or large and spirally twisted, e.g. Limnaeus, Helix. Includes (i) 

 Basommatophora ; eyes median at base of tentacles; male and female genital 

 orifices separate but near one another ; aquatic ; e. g. Limnaeus, Planorbis, Ancylus, 

 Auricula ; (ii) Stylommatophora, eyes elevated on invaginable tentacles ; shell either 

 large or spirally coiled, or minute, or absent; edge of branchial fold of mantle 

 always fused to neck, leaving a pulmonary aperture ; mostly terrestrial, e. g. Helix, 

 Pupa, Clausilia ; Testacella, Limax, Arion ; Onchidium. 

 See literature, pp. 109, 112, 118, 123, 283. 



Haliotis, Wegmann, A. Z. Expt. (2), ii. 1884. Patella, Harvey Gibson, 

 Trans. Roy. Soc. Edinburgh, xxxii. pt. 3, Session 1884-85; development of, Patten, 

 Arb. Zool. Inst. Wien, vi. 1886. Anatomical points in Fissurella, Haliotis, Tro- 

 chidae, Haller, marine Rhipidoglossa, M. J. ix. 1883. Vermetus, de Lacaze Duthiers, 

 A. Sc. N. (4), xiii. 1860. Pleurobranchus, Id. op. cit. (4), ix. 1859; cf. A. G. 

 Bourne, Q. J. M. xxv. 1885. Non-palliate Opisthobranchia, Bergh, Challenger 

 Reports, x. 1884 (with lit. referred to); Trinchese, Atti Acad. Lyncei (3), xi. 

 1 880-8 1 ; cf. British Nudibranchiata, Alder and Hancock, Ray Soc. 1845. 

 Onchidium, marine, slug-like Pulmonate, Bergh, Challenger Reports, x. 1884, 

 Appendix, p. 126; and M. J. x. 1885. Structure and development of O. celticum^ 

 Joyeux-Lamiie, A. Z. Expt. x. 1882. 



Glands of mantle margin in Aplysia, Blochmann, Z. W. Z. xxxviii. 1883. 

 Purple gland hypobranchial gland of Purpura, de Lacaze Duthiers, A. Sc. N. 



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