308 
MR. WILSON ON THE STRUCTURE AND DEVELOPMENT OF 
The flask-shaped flattened organ terminates posteriorly in a narrow elongated pro- 
cess which is received between two oval, flattened organs within the head, and these 
latter are connected with two large reniform organs which constitute the bulk of the 
head. Moreover, it is to these oval-shaped organs that the muscular apparatus in- 
tended to retract the head is attached. The oval-shaped organs are marked in the 
middle by a small indistinct circle, and on each side by a dark spot, produced appa- 
rently by a deposit of pigmentary matter. 
On the under surface of the head in the middle line, and occupying the anterior 
half of its length, is an oblong opening, the mouth ; it is surrounded in front and on 
the sides by a broad and raised border, consisting of a number of tentacula, four 
pairs of which may be distinguished as being superior and three inferior. There are 
consequently no less than sixteen tentacula surrounding the aperture of the mouth ; 
the central pair, or antennse-like tentacula, proceed, as I have before remarked, by 
the side of the neck of the flask-shaped organ, while the four remaining pairs appear 
to originate from the under surface of that organ. The three pairs of inferior tenta- 
cula are productions of the integument from the posterior boundary of the mouth, 
the external pair being the longest, and the innermost pair merely rudimentary. 
Behind the mouth the boundaries of the pharynx are seen through the transparent 
integument. 
The tentacula are capable both of lateral and central approximation, and by these 
movements effect a closure of the aperture of the mouth. They cooperate in the act 
of prehension and detention of food, and by their close contact constitute a tem- 
porary haustellum by which the fluids of the nutritive mass are expressed and 
imbibed by the animal. 
Immediately within the tentacula are situated a considerable number, probably 
from four to ten pairs, of maxillae which form an internal border to the mouth. The 
maxillae are elongated cylindriform organs, projecting by their free extremity one 
beyond the other along the border of the mouth, from its posterior to its anterior 
boundary, and corresponding by their axes with that of the head. They are appa- 
rently attached to the pair of large reniform bodies which form the principal bulk of 
the head, and by their shafts constitute the walls of the pharynx. 
The maxillae, like the tentacula, are capable of close approximation, both in the 
lateral and central direction, and are consequently well adapted to assist the latter 
in the office of suction, and at the same time to masticate substances presented to 
them by the tentacula. In the latter action the tentacula would hold the nutritive 
substance, while the maxillae are engaged in its trituration and deglutition. 
Within the head, and constituting the bulk of this part of the animal, are two oval- 
shaped or reniform bodies of an opake white colour. These bodies are slightly 
flattened from above downwards in conformity with the shape of the head ; they are 
broad in front, somewhat narrower behind, where they are separated by a narrow 
interspace, convex on their outer border, and flattened on the middle line. In the 
