18 Prof. J. C. Schiodte on the Structure of 



situated ; this latter consequently projects downwards inside 

 the mouth -tube, just behind the labrum, and beneath the 

 corresponding lobe of the tongue, which forms the bottom of 

 the mouth-tube. The lobe of the mandible [m, fig. 4 c) is 

 elongated triangular, gradually acuminated, with convex back 

 and concave front, the sharp lateral edges meeting at the 

 sharp-pointed hooked apex. The muscles of the lobe fill the 

 greater part of the stem in front of the insertion of the palpus. 

 This arrangement, in connexion with the corresponding great 

 length of the stem, indicates great power and perseverance of 

 movement, and explains how these lobes, in spite of their 

 inconsiderable size, may be used with great effect. Their 

 shape and position enables the animal to sink them into its 

 victim, one from either side, in slanting converging directions, 

 and then, by drawing them back simultaneously with sufficient 

 strength, to tear out the piece which lies between them. That 

 they are destined to work against each other and to be drawn 

 back together is plain from the circumstance that their points 

 are not quite uniform, the left hook being somewhat more bent 

 than the right one, and at the same time a little twisted to the 

 side, so that it can take hold round the other. 



The sawing-styles, or maocillce of the first pair ^ consist each of 

 a shorter stem and a longer lobe, which joins the former evenly 

 all round. They are hard, smooth, slightly flattened, and bent 

 inwards, so that their ends project downwards in the mouth- 

 tube, behind the mandibular lobes, under the tongue, and on 

 either side of the buttonhole-shaped sucking-slit. The sfeven 

 hooked spines at their apex are so placed as to form a curved 

 group ; and it is therefore difficult to make out their form and 

 number except when the lobe is pressed. These sawing-styles 

 are evidently intended to act as auxiliary instruments, for 

 deepening, increasing^ and lacerating the wounds made by the 

 mandibular lobes. 



The long and slender mandibular 'palpi (fig. 4 a) are, when 

 at rest, placed firmly against the head in a groove on the 

 underside of the skull, which runs at a little distance from the 

 stem forwards between the forehead and the posterior antenna?, 

 round the basal joint of which their pointed and sickle-shaped 

 terminal joint coils itself. The palpi, being inserted so far be- 

 hind and to the side that they have considerable room for play, 

 are probably destined for cleaning the mouth-tube with the 

 brush at their apex, and to comb away the fishy slime from 

 the marginal hooks by means of the fine comb of spines im- 

 planted in the outer margin of the terminal joint. 



The structure of the mouth, in ^ga may therefore be de- 

 scribed in the following terms : — 



