254 APPENDIX. 



aperture in the extremity of which just allows their points to protrude. Each 

 of these broad fleshy lips is crossed by transverse parallel plaits or folds of 

 membrane, about twenty-five in number, which in their free margin exhibit 

 a delicately notched appearance, and in fact in every particular resemble a 

 similar structure which is seen on a larger scale in the sucking disc situated 

 upon the dorsum of the head of the Hemora, by which that fish is enabled to 

 attach itself firmly to various objects. In the present instance, however, 

 the structure, though precisely similar, is exceedingly delicate, and so 

 minute as to be invisible to the naked eye, though there can be no doubt 

 that it is intended to answer the same purpose in both. For by the aid 

 of this sucker the larva is enabled to fix the head, so as the more readily 

 to insert its sharp hook-shaped mandibles into the soft mucous membrane 

 of the intestine which it inhabits, and draw therefrom its nutrient juices, 

 which would thus readily flow into the little aperture of the mouth, 

 situated in the centre between the mandibles, assisted also by the partial 

 vacuum which would thus be produced during the act of adhesion. 



" The mandibles are sunk so deep between the two fleshy lips, having 

 only the points projecting from the aperture of their investing sheaths, 

 that it is necessary to disconnect them entirely from the soft parts before 

 they can be accurately examined. They are placed parallel to each other, 

 with their hooked points directed downwards, so as the more readily to be 

 inserted. The mandibular apparatus on each side consists of three portions. 

 The first portion is hooked and sharp pointed, and is only the g^th of an 

 inch in length. It is nevertheless furnished at its base with a delicately 

 shaped ball, adapted accurately to a socket in the second joint, and has 

 projecting from either side of its base a sharp spine or trochanter, for the 

 insertion of the tendons of the abductor and adductor muscles by which its 

 movements are effected. The second joint bears the socket to which the 

 ball of the first is adapted, and at its opposite extremity is united to the 

 third and principal portion of the jaws, which consists of a broad expanded 

 corneous plate, of less density than the preceding, and resembling in form 

 and office a similar structure well known as occupying the centre of the 

 large claw of the lobster, being for the attachment of the muscles by 

 which the mandibular hooks are moved to and fro. The whole man- 

 dibular apparatus measures about ygth of an inch in length, and, being 

 very firm and solid, presents a remarkable contrast in texture to the 

 surrounding soft parts with which it is connected, and from which it 

 is easily detached. 



" If the body of the insect be laid open the alimentary canal is seen 

 to be of considerable length, and much convoluted. It commences by an 

 exceedingly delicate hair-like oesophagus, so narrow that it would appear 

 to be specially destined to transmit fluid nourishment, and nothing else. 

 This terminates about the third segment of the body in a minute globular 

 cavity or proventriculus, which is of the same diameter as the rest of the 

 alimentary canal, and immediately below whic'h four very short salivary 

 vessels enter. From this point commences the large intestiniform sto- 

 mach, which after contracting in its first third to the finest thread, 

 again dilates and proceeds of uniform diameter to the point where 

 the four slender biliary vessels enter, where it again contracts and 

 forms a short intestine. The whole alimentary canal is about six times 

 the length of the body, and of this length the stomach forms about five 



