LINGUATULA FEROX. ]3 



obtuse angled and emarginate. From this point they narrow 

 rapidly towards the apex. They exhibit double contours,, are 

 hollow internally, and lie for the most part in an inversion of the 

 ventral skin. Each of these hooks is borne by a peculiar chiti- 

 nous apparatus of support. The latter consists of a sort of furrow 

 or fork, the stem of which is bent in the form of a hook, becomes 

 constantly more diminished and curved posteriorly and towards 

 the free apex, but widens anteriorly. This broader portion divides 

 into two sections uniting at an acute angle. The portion turned 

 from the ventral side and directed outwards, divides into two 

 broad, forked lamella^ which receive the base of the true claw 

 between them, and allow it to swing. The massive portion of the 

 stem directed upwards and inwards ceases at this point at the same 

 level with the lamellae of the fork, and becomes converted, as it 

 appears to me, into a very thin filament, which, as it were, furnishes 

 the skeleton or point of support for two lateral lobes, which are 

 nothing but two lobes of the ventral skin. These lobes are pro- 

 duced by the impression which the convexity of the hook- 

 apparatus forms from the ventral skin towards the dorsal and into 

 the ventral skin. They are only the mechanical consequences of 

 this impression, and assist in forming the anterior part of those 

 peculiar structures, which the authors describe as cleft-like open- 

 ings, and which have led to their being confounded with a mouth. 

 Whether this delicate chitinous threader ridge is really there, or, 

 as Zenker, for example, thinks is not present, others may decide; 

 it is not indispensably necessary, for the convexity of the hook 

 itself might certainly hold the skin upright and stiffen it in the 

 median line of the lobes. Quite in front, and at the point where 

 the sides of the lobes of skin again unite with the flat tissue of 

 the ventral skin, there is a small chitinous structure, which, so to 

 speak, looks like a three-cornered hat in minima. This little 

 body has a cavity which is directed downwards and outwards, and 

 a closed convexity or cover which is turned -towards the ventral 

 membrane. In front there is a little beak, exactly like the 

 anterior handle of a three-cornered hat. This little beak usually 

 stands straight out and downwards ; by force and strong pressure 

 it may acquire all sorts of different forms, and, for example, bend 

 into a hook. I have formerly given this last-mentioned structure 

 the name of the " Navicula ;" J. Miiller, when I explained to him 

 the mechanism of the movements of the hooks of Linguatula, gave 

 it the very characteristic name of the "point-cover" (Spitzendecker). 



