Dr. Johnston on Scottish Mollusca. 51 



cles of a bluish colour \ its margin entire, somewhat undu- 

 late, overlapping. Space between the cloak and foot white or 

 yellow, smooth ; the foot varying from pale yellow to an orange, 

 plane and broad. Dorsal tentacula conical, short, the upper 

 half yellow and lamellate *, the base white and smooth, issuing 

 from sheaths level with the surface. Branchiae of 8 large tri- 

 pinnate plumose leaflets, some so deeply divided that the leaf- 

 lets appear to be eleven or twelve f, of a light blue colour ir- 

 regularly spotted with white and yellow about their bases. 

 Anus prominent, tubular, whence, in many specimens, lines of 

 a sulphur colour diverge to the branchiae. 



When handled the cloak has a cartilaginous somewhat gritty 

 feel, from containing in its texture a vast number of crystalline 

 spicula, clustered more especially in the tubercles. These spi- 

 cula are cylindrical, slightly curved, obtuse at both ends, some- 

 times bulged about the middle, colourless, pellucid and calca- 

 reous, for they dissolve readily in weak acids. Similar spicula 

 are to be found in the tentacula radiating from the centre, in 

 the branchiae and in the foot ; but less thickly set than in the 

 cloak, and perhaps less regular in their figure. 



D. tuberculata is a very sluggish creature. When kept in 

 a vessel until the water becomes unfit for respiration, it dis- 

 charges, in dying, a large quantity of a gelatinous fluid from 

 the skin, and some dirty greenish liquor from a small aper- 

 ture placed before and a little to the right of the anus. This 

 is the orifice of a duct which takes its origin from the liver, so 

 that this viscus, besides the bile, appears to prepare another 

 excremental secretion, that may, perhaps, be of use to the ani- 

 mal in rendering it disagreeable to its enemies. Of such a 

 combination of functions there is no other example among 

 animals, and the fact was so strange and anomalous that re- 

 peated careful dissections were required to convince Cuvier of 

 its reality ; and, after no further doubt could be entertained, 

 he suggested a possibility of two glands being here so inti- 



* Cuvier says, these tentacula " sont toujours composes de petits feuil- 

 lets extraordinairement minces, empiles les uns sur les autres, et comme 

 entiles dans un pedicule commun." — Mem sur le Doris, p. 12. 



f Rapp, under his description of Doris gr audi flora, says that the number 

 of branchial leaflets cannot be used as a specific character, because they 

 vary considerably in this respect in different individuals. — an observation 

 which I believe to be applicable to the genus. 



E 2 



