248 Mr. Baird on British Entomostraca. 



other naturalists after him, call them antennas. Jurine, 

 however, calls them " bras ramifies/' and Straus, considering 

 them very justly as the chief or almost only organs of loco- 

 motion, and acting as it were as fins, calls them rami, or 

 rames branchues : they are in fact, he says, a first pair of feet, 

 and act as such ; as it is by means of these organs alone that 

 the insect moves, the other feet not serving at all for that 

 purpose. 



The brain, or first ganglion of the nervous system, is situ- 

 ated near the eye, and is composed of two lobes, from the 

 superior anterior commissure of which we see, going off to 

 the eye, the optic nerve. The mouth is of a rather compli- 

 cated structure, is situated near the junction of the head and 

 body, near the base of the beak, and consists, according to 

 Straus, who has given the most correct account of this organ, 

 of a "labre" or lip, two mandibles, and one pair of jaws. The 

 "labre" or lip (plate ix. fig. 3.) consists of a flattish body, 

 strongly compressed at the sides, and has at its extremity a 

 large lobule (a). It is fixed to the posterior part of the base 

 of the beak, is very moveable upon its antero-superior angle, 

 and admits of a considerable separation. The mandibles 

 (plate ix. fig. 2.) are very strong, and consist each of a pretty 

 broad plate, which at its superior extremity is in form of a 

 narrow point (a), and articulates there with the body. It de- 

 scends from thence vertically to the mouth, its inferior extre- 

 mity being curved sharply inwards, so as to penetrate into the 

 mouth between the labre and corresponding jaw, and termi- 

 nating in a sharp, simple, cutting edge (b), which has neither 

 teeth nor triturating surface, and is quite free and unattached. 

 These mandibles are not provided with either palpi or bran- 

 chiae, but are quite naked, and are moved by two muscles ; an 

 abductor which moves them upon themselves from within 

 outwards, and an adductor (c) which brings them back to 

 their first position, and at the same time bringing them nearer 

 each to the other. The jaws (plate ix. fig. 1.) consist each of 

 a strong body (a), somewhat in the form of a disc, or rounded 

 on the posterior surface and a little flattened on the sides, 

 which terminates in four strong, horny spines (c c), three of 

 which are prolonged into hooks, which are strongly curved 



