1819.] NATURAL SCIENCES OF PHILADELPHIA. 105 



the whole length of the everted penis, with several irregular dila- 

 tations and constrictions through the posterior part, and ending 

 on the blunted point of that organ with a small round orifice. 

 The spermato-duct is attached to the walls of the penis by 

 abundant connective tissue; its wall is very thick ; the inside in 

 the posterior part with some strong longitudinal folds, clothed 

 with a fine epithelium, which towards the end of the penis is about 

 0.07 mm. in thickness. The (PI. III. fig. 13(/) penis, as above 

 stated, flagelliform, about 20.0 mm. long, under the loop fur- 

 nished with a whitish covering, partly confluent, partly scattered; 

 in the skin through the whole length of the organ an infinity of 

 bottle-shaped, glistening glands about 0.035 to 0.04 mm. in length. 

 The spermatotheca pyriform, about 9 mm. long, passing without 

 precise limit into a short ductus, that is a little dilated in the 

 inferior part (vagina). The large mucous gland convex in front; 

 on the back rather flat toward the anterior part, in the posterior 

 excavated (for the reception of the ampulla of the hermaphroditic 

 duct); the duct short; the cavity of the organ narrow, empty. 1 



DORIDIDiE. 



This large group is easily distinguished through the (retractile 

 or not retractile) branchial rosette on the middle of the back. 

 This character is only found in a single other group of gastero- 

 poda, the Doriopsidse, which, in their exterior characters, closely 

 simulate the Doriduhe, and had been confounded with them, at 

 least so far that the}' were regarded as both belonging to a single 

 large group, until my examination of them'- showed their affinity 

 to the Ph yllidiidee* with which they were combined by me in a 

 larger group, the Porostomata, particularly characterized through 

 their poriform "outer mouth," and the conversion of the bulbus 

 pharyngeus into a quite unarmed sucking apparatus. On the 

 contrary the Dorididae all show a very well-developed bulbus, 

 with a more or less strong tongue; and often also a particular 

 armature of the lip-disk on the anterior end of the bulbus, and 



1 Pallas (1. c. p. 238, fig. 23*b) seems to have seen different parts of the 

 anterior genital mass. 



2 R. Bergh, neue Naektschnecken der Sudsee. Journ. der Mus. Godeffroy. 

 Heft viii. 1875, pp. 82-94, Taf. x. xi. 



3 R. Bergh* Beitr. til Kundsk. om Phyllidierne (Schiodte) Natur. Tidsskr., 

 3 R. v. 1869, pp. 357-543, tab. xiv.-xxiv. 



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