208 MESSRS. HANCOCK AND EMBLETON ON THE ANATOMY OF DORIS. 
results by comparative dissections, we feel more confidence in placing on record an 
extended account of our researches. 
Before we commence the anatomical description, we may premise that for exami- 
nation, we have selected D. tuberculata, not only as the species most highly typical 
of the genus, but as that which, on our coast, is the most abundant and the largest, 
and therefore in all respects most convenient for our purpose. We have not however 
confined ourselves to this single species, but have examined several others, with a 
view of obtaining a more accurate knowledge of the anatomy of the genus. Of these 
latter we may mention D. pilosa and D. hilamellata, as representing very fairly, with 
D. tubei'culata, the three great divisions which have been characterized in the 
Monograph on the British Nudibranchiata, now in course of publication by the Ray 
Society. 
D. tuberculata is 2 or 3 inches long, pretty regularly oval, rather depressed, arched 
above, with the mantle extending over the whole back, concealing the head and foot, 
and covered with numerous obtuse, spiculose tubercles of various sizes ; the dorsal 
tentacles are retractile within cavities, of a clavate form, with the upper portion 
laminated : the mouth projects a little in front between the foot and mantle ; on each 
side is a small depressed, obtuse, angular tentacle : there are nine branchial plumes 
united at the base, and retractile within a cavity ; they form a circle on the median 
line of the back near the posterior extremity, enclosing the anal and renal orifices ; 
the foot is broad, truncated in front, and rounded behind : the genital orifice is 
situated towards the anterior extremity, on the right side, between the mantle and 
foot. 
D. pilosa differs from D. tuberculata chiefly in having the back more elevated, and 
in being clothed with soft conical papillae ; the oral tentacles too are fused into a veil, 
which is at either side expanded into a leaf-like process, and the branchial plum.es are 
non-retractile, being merely contractile. This species is about 1 inch long. 
D. hilamellata is not more than three-quarters of an inch in length, and is consider- 
ably depressed, having the mantle covered with large, spiculose tubercles : branchiae 
of about twenty, simply pinnate, non-retractile plumes, set separately in an open 
circle : head furnished with a semicircular veil. In other respects this does not 
differ materially from the above species. 
Digestive System . — On removing the skin of the back, the viscera, including the 
buccal apparatus, are seen bound down and completely covered by a transparent 
fibrous membrane, which is fixed on each side to the inner surface of the skin just 
above the track of its great lateral venous canals, and to the circumference of the 
pericardium. For want of a better name we call this membrane the peritonseum. 
It has been removed to show the viscera*. The mouth opens on the inferior surface 
of the body between the cloak and the foot ; it is surrounded by a protuberant, fleshy, 
outer lip divided below on the median line. The channel to the buccal cavity is very 
* Plate XI, fig, 4, and Plate XII, fig, 1, 
