82 
THE VOYAGE OF H.M.S. CHALLENGER. 
the body there were only a few hardened cells, with the exception of that surrounding 
the main ducts of the genital apparatus, where there were a number of cells similar to, but 
rather larger and darker than, those found in the neurilemma. 
The mouth tube is strong, about 5 mm. in length ; its inner surface and the three 
retractor muscles are as usual. The bulbus pharyngeus is 5 ‘5 mm. long by 5'3 in 
breadth and 4 ‘5 mm. in height; the radula-sheath, moreover, projects backwards about 
2 mm. ; the retractor muscles as usual. The strongly arched labial disk (PI. II. fig. 14) 
is covered on its inner half by the rather thick yellow labial plate, clothing the "anterior 
portion of the buccal cavity to a breadth of about 1 mm. with a circular prehensile ring. 
The labial plate is made up of hook-shaped rods thickly adpressed at the ends, which 
in front (PL III. fig. 16) reach a height of ‘04 mm. The broad, strong tongue has the 
usual deep cleft, which is clothed up over the margins by the clear yellow, somewhat 
feebly coloured radula. In this last were twenty- eight series of teeth (counted always 
at the outer margin of the radula) ; further back there were forty-five developed and 
four undeveloped series ; the total number was thus seventy- seven. The first three rows 
of the tongue were very incomplete, and in front of them were the impressions left by 
two or three other series that had fallen off. On the narrow rhachis (PI. III. 
fig. 17, a, 20, aa) were long, narrow, very low folds. In the fifth row of the tongue there 
were on either side 172 or 173 teeth, at the root of the tongue 186, and the number 
appeared to increase on passing back in the sheath to 200. (In another smaller speci- 
men formerly studied by me, 1 there were 80, and in larger specimens 97-104 series of 
teeth ; the smaller individual had 170 teeth in each series, the larger individuals as 
many as 239.) The teeth were of a clear yellow colour; the height of the outermost 
generally '05 mm., the height of the plates increasing to ’12 mm. The innermost (PI. III. 
fig. 17, bb) is provided with a small denticle below on the inside of the hook, and in a 
few of these teeth a higher magnifying power (750 diam.) showed also traces (fig. 17, bb) 
of two smaller ones ; on the outer side of the same innermost plate, a little higher up, 
was a similar denticle (fig. 20, bb). In all the following ones, as far as the outermost 
(inclusive), this outer denticle was present (PI. III. fig. 19), and only appeared to be 
absent here and there in single plates. Elsewhere the teeth showed the ordinary form; 
the three or four outermost ones were as usual smaller and more upright, with the 
denticle near the point of the thick hook (PL II. fig. 15, aa). 2 
The salivary glands band-like, whitish in colour, extended to the length of 15 mm.; 
the breadth was mostly ‘8 mm., but they were narrower behind; they extend, 3 as already 
described, as far as the cardia. The duct was rather short, about 1 mm. in length. 
The oesophagus is mostly about 1 cm. wide, wider still behind ; it opens into the stomach, 
and receives behind the wide bile duct. The stomach is 9 mm. long by 4 '5 mm. in 
1 Loc. cit., p. 397 
2 The series of teeth of the specimen examined here were, as in Ceratosoma, gracillimum (loc. cit., p. 404), nearly all 
denticulated, whicli was not the case in the specimens formerly dissected by me. 3 Loc. cit., 1876, p. 399. 
