26 A MONOGRAPH OF THE 



Monstrosities, or sports of nature, are occasionally found amongst the Nudibranchiata, Mr. 

 Peach sent us from Peterhead an Eolis papillosa, in which there was only one dorsal tentacle, 

 placed in the centre of the head. Sir J. G. Dalyell figures the tentacles of an Eolis, which he 

 calls E. monoceros, from the circumstance of its having a single forked dorsal tentacle. "A 

 pillar," he says, "rises from the middle of the neck, which diverges into two cornicula, with 

 about seven whorls on each. 1 ' It was probably a monstrosity of E. coronata. In both these 

 instances, the peculiarity appears to arise from the complete or partial fusion of the two ten- 

 tacles into one. The latter author also figures a mal-formation of Botofragilis (called Tritonia 

 coniferd) with " a large central branchial tuft on the back between the two branchiae of the 

 third pair." We have seen Eolis rufibranchialis with one of the dorsal tentacles bearing a 

 lateral branch ; and have observed a similar sport of nature in the branchial papillae of E. alba 

 and several other species. More frequently, however, the variations consist of the suppression 

 of less important parts, to which some species are more liable than others. Polycera quadri- 

 lineata is extremely variable in this respect ; the velar filaments, the rows of tubercles, and 

 the branchial appendages being alike subject to variation in this species. 



Parasites. — The Nudibranchs are frequently infested with parasitical Entomostraca, 

 which are usually buried beneath the skin, the ovigerous vesicles only appearing outside ; but 

 occasionally they penetrate into the abdominal cavity, or live freely on the surface. We have 

 observed several species of these parasites inhabiting the Dorididcs and Eolididce. 



Tetliys is liable to be thus annoyed by a large kind ; an individual so affected is figured 

 in Delle Chiaje's Memoirs, (copied in Mrs. Gray's 'Figures of Molluscous Animals,' pi. 210, 

 fig. 1). A small species is occasionally found on some of the Eolides and on Doto coronata. In 

 two or three specimens of Eolis rufibranchialis which occurred near Whitley, two irregularly 

 formed elliptical lobes, the ovigerous sacs of this species, protruded from the skin between the 

 tentacles. The Eolides were apparently quite healthy, and evinced no suffering, notwithstanding 

 that the parasites .must have been lodged in the vicinity of the cephalic ganglions. The lobes 

 were very dense, pale flesh-coloured, and exhibited a minute granular appearance. The 

 second day after their capture the lobes disappeared, and in the course of an hour or two they 

 were replaced by others, in which the granular appearance was very indistinct. Unfortunately, 

 we have not been able to examine the body of this animal sufficiently to give a description of 

 it. Two very curious forms, however, have occurred in some specimens of Doris pilosa from 

 Devonshire, to which we have paid more attention. Both these were found within the abdominal 

 cavity resting upon the liver-mass. One (PI. 45, figs. 6, 7) is nearly a quarter of an inch long, 

 with a narrow, linear, soft body, of a white colour, without segments, and having the tail or 

 abdomen tapering a little, and apparently composed of two or three articulations. This 

 extremity is always attached to the skin within the branchial circle of the Boris, where 

 the ovigerous lobes were most likely protruded. These, however, we have not seen ; though 

 in one specimen, what appeared to be the remains of them, were still adhering to the tail. 

 There are three pairs of legs from the sides of the body, which are long, tapering, soft, and 

 without articulations ; they lie closely embracing the liver-mass. The mouth is situated below 

 in front, and is apparently without appendages. 



We have never found more than one individual of this strange form inhabiting the same 

 Doris; and with it there were always associated one, two, or three of the other species before 



