794 CLASS xin. 



three branchiae, two or a single one, composed of numerous leaves, 

 arranged parallel like the teeth of a comb. 



Very rarely, in place of branchiae a vascular network in the walls 

 of respiratory cavity. Sexes separate, external organs of copula- 

 tion distinct. 



Pectinibranchiates. In all two feelers and two eyes are present ; 

 these last are often pediculate. The mouth has the form of a pro- 

 boscis, of which the structure has been described at length by 

 CUVIER in the whelk (Euccinum). It consists of two tubes, which 

 push one into the other and are connected together by the upper 

 margin, so that when the innermost tube is unrolled and elongated, 

 the outermost becomes shorter. This instrument is moved by many 

 muscles 1 . The hinder part of the body contains the liver and the 

 sexual organs. The sexes are distinct. In the male the penis is 

 situated on the right side, behind the head, and in some, as in the 

 whelk, is very large. It is folded round and concealed in the respi- 

 ratory cavity, but is not retracted within the body, except in the 

 genus Pcdudina, where it is protruded and retracted through an 

 aperture in the right tentacle, which had been observed already by 

 LISTER, but was afterwards incorrectly denied by DRAPARXAUD. 

 Through the penis runs a tortuous canal, which on copulation, 

 when that organ is erected, probably loses its tortuosities. Ac- 

 cording to B ASTER and BLAINVILLE, the shells indicate a difference 

 of sex, and those of the female are wider, particularly in the last 

 wreath 2 . 



The females secrete a kind of common envelope for the eggs, 

 which they deposit at the same time with the eggs. On our shores 

 round clumps of yellow vesicles may be frequently observed, which 

 resemble bunches of grapes, and are the masses of whelk's eggs in 

 question 3 . According to CUVIER, this envelope is secreted by a 



1 Ann. du Mus. xi. 1808, Memoires s. 1. Moll. No. 17, pp. 6, 7, figs. 8 10. 



2 See EASTER NatuurTc. Uitsp. I. bl. 39, 40; BLAINV. Journal de Physique, xciv. 

 p. 92; MECKEL'S Archiv f. d. Physiol. vn. s. 571573, 1822. EASTER says that in 

 JBuccinum the shell of the male is somewhat smaller, that it has a greater number of 

 wreaths, but which are thinner than those of the female. 



3 See figures of them in EASTER NatuurTc. Uitsp. i. Tab. v. figs. 2, 3 of Buccinum 

 undatum; Tab. VI. figs, i 3, of a species of Murex. Comp. ibid. bl. 3845; see 

 also LUND Recherches sur les Enveloppes d'ceufs des Gasteropodes pectinibranches, Ann. 

 des Sc. nat., 2e Se*rie, I. Zoologie, pp. 84 112. By ARISTOTELES these masses of eggs 

 are called fjt,e\tK^pat (translated favayines) ; he did not, however, suppose that shelled 



