DORIS. 



between the cloak and the foot in front, and is furnished with two oral tentacles, very -variable 

 in shape, sometimes linear, sometimes tubercular or flattened, and sometimes their place is 

 supplied by a veil, which surrounds the head, and may be considered a modification of these 

 organs. The mouth is occasionally slightly protuberant; it is most commonly without jaws, 

 but sometimes very rudimentary ones exist; and it is frequently furnished with a spinous 

 prehensile collar at the buccal orifice. The tongue is denticulated. Doris was long supposed 

 to be without eyes. Those organs, however, are always present ; but in most cases must 

 perform the function of vision very imperfectly, as they are seldom to be seen through the 

 skin excepting in some very transparent species, or in very young individuals. There are 

 two dorsal tentacles, which are placed on the cloak in front, and at some little distance from 

 the margin ; their form is generally linear or clavate, the upper portion being always 

 laminated ; they are retractile within cavities, the margins of which are sometimes produced 

 into short sheaths. The branchiae are plumose and surround the anus, which is situated 

 posteriorly on the central line of the back. They consist of several plumes, sometimes small 

 and simple, sometimes large, and more or less branched ; and are either united at the base 

 into a flower-like expansion, or placed separately in a circle, more or less broken posteriorly. 

 In the typical division of the genus, these plumes are retractile within a common cavity, the 

 margin of which is capable of being closed completely over them, so as to protect them from 

 danger. In those abnormal species that form our second and third sections there is no 

 cavity; the plumes are consequently not retractile, but contractile only, being, in their 

 contracted state, curled up, and drawn closely down on the surface of the cloak. The foot is 

 flat disc of an oblong form. The aperture of the sexual organs is single, and situated an- 

 teriorly on the right side between the cloak and the foot. 



We are inclined to believe that the Dorides are carnivorous ; but this fact has not been 

 sufficiently investigated. D. tuberculata has been detected feeding on Halichondria panicea, 

 and Grantia compressa, and the stomach of this species is almost always found filled with 

 fragments of the former sponge. It is likewise worthy of remark, that D. depresses,, D. sparsa, 

 and D. inconspicua are found adhering to calcareous zoophytes, on which there can be little 

 doubt that they feed. 



This genus has a wide geographical range, species occurring from the frozen to the 

 torrid zones, and in every quarter of the globe. In depth it extends from the littoral to the 

 coralline zone ; but is most abundant in the littoral and laminarian. Some species are found 

 equally abundant in both these zones ; and in particular D. pilosa may be mentioned. This 

 species has a peculiar structure within the stem of the branchial leaflet highly developed, 

 giving the cha acteristic star-like appearance in the centre of the branchial circle. The 

 structure just alluded to is also found in D. tuberculata. It is composed of a series of irregular 

 cells with thickish elastic walls, and is apparently intended to give reciliency to the branchial 

 plumes, keeping them to some extent expanded, even when out of water, and thus, perhaps, 

 certain species may be enabled to extend their range to within tidal marks. 



Ehrenberg made an attempt at a redivision of this genus in his ' Symbolse Physicse,' 

 published in 1831 ; his arrangement, however, does not include the whole of the forms 

 contained in the genus, but appears to be confined to the species that had come under his 

 observation. He restricts the genus to those species (not otherwise distinguished) which have 

 the branchiae retractile within a cavity, and divides them into the following sub-genera. 



