828 MANUAL OP THE MOLLUSCA. 



sinuses in tlie skin, from which it returns to the auricle by two 

 lateral veins, without having circulated through the gills. The 

 heart is contained in a pericardium to which is attached a small 

 ventricle, or portal heart, for impelling blood to the liver ; the 

 hepatic veins run side by side with the arteries and open into a 

 circular vein, surrounding the vent, and supplying the gills. 

 Only hepatic blood, therefore, circulates through the gills. In 

 u^olis there are no special gills, but the gastro -hepatic papillse 

 are accompanied by veins which transmit blood to the auricle. 

 The skin acts as an accessory breathing-organ ; it performs the 

 function entirely in the Elysiadoe, and in the other families, when 

 by accident the branchiae are destroyed. The water on the gills 

 is renewed by ciliary action. The fry is provided with a trans- 

 parent, nautiloid shell, closed by an operculum, and swims with 

 a lobed head-veil fringed with cilia, like the young of most 

 other gasteropods. (Hancock and Embleton, Phil. Trans. 1852. 

 An. Nat. Hist. 1843.) 



Family VI. — Dorid^.* Sea-lemons. 



Animal oblong; gills plume-like, placed in a circle on the 

 middle of the back ; tentacles two ; eye-specks immersed, 

 behind the tentacles, not always visible in the adult ; lingual 

 membrane usually with numerous lateral teeth, rachis often 

 edentulous ; stomach simple ; liver compact ; skin strengthened 

 with spicula, more or less definitely arranged. 



Doiiis, L. 



Etymology, doris, a sea-nymph. 



Example, D. Johnstoni, PL XIII., Fig. 1. 



Synonyms, Dendrodoris, Eb. Hemidoris, Strp. 



Animal oval, depressed; mantle large, simj)le, covering thehead 

 and foot; dorsal tentacles 2, clavate or conical, lamellated, retrac- 

 tile within cavities ; gills surroimding the vent on the posterior 

 part of the back, retractile into a cavity ; head with an oral 

 veil, sometimes produced into labial tentacles ; mouth with a 

 lower mandible, consisting of two horny plates, united near 

 the front, and having 2 projecting points ; lingual teeth nume- 

 rous, central small, laterals similar, hooked and sometimes 

 serrated, 24-68 rows; 37-141 in a row; nidamental ribbon 

 rather wide, forming a spiral coil of few volutions (p. 41, 

 Fig. 29). 



* Contracted from Dorididce ; aa tlie Greeks used Deucalides for ZJeMcaZionfiirfc*. 

 Ehrenberg divided the genus Doris into sections by tlie number and foma of the gills, 

 characters of only specific importance. 



