5*20 History of Britisli Entomostraca. 



tennae are, but yet he does not mention the long filaments which they 

 possess, and by which their action, as fins, is principally produ- 

 ced. They are considered by Latreille as acting, along with the an- 

 tennae, as respiratory organs. The second pair of feet (Fig. \.f. Fig. 

 4,) are not so strong as the first pair, and are composed of five articu- 

 lations also, the last of which is terminated by one strong curved 

 hook. The first pair are directed backwards ; the second are direct- 

 ed forwards ; they want the long filaments which the first pair pos- 

 sess, and are thus only used for walking with. The third pair (Fig. 

 1. g. Fig. 5,) arise immediately behind the second pair, and consist 

 of four articulations;* the last of which is terminated by two short 

 hooks, and has a filament thrown back from its extremity, like a 

 spur. They are curved upwards and backwards, and are always 

 contained within the shell, never being extruded. Their use, ac- 

 cording to Straus, is to support the ovaries. Jurine considers them 

 as somehow connected with the matrix, but says he is ignorant of 

 their use ; the figure which he gives of them is very incorrect. 

 Mouth The mouth is situate in the inferior surface of the ante- 

 rior lobe of the body, and consists of a lip, a kind of sternum,t per- 

 forming the functions of an inferior lip ; a pair of palpiferous man- 

 dibles, and two pairs of jaws. The lip, (Fig. 6, a.,) says Straus, is 

 composed of a great scaly piece like a hood, forming a projection 

 which advances between the two anterior feet, and is fixed to the 

 body by four long apophyses. The sternum, or lower lip, (Fig. 6. 

 b.) according to the same author, is elongated, triangular, and move- 

 able, articulates with the lip, and has at its extremity two curved 

 apophyses to articulate it with second pair of jaws. The mandible 

 (Fig. 7- g- Fig. 1. h,) is very large, and is formed of two pieces. The 

 larger, or mandible, properly so called, (Fig. 7- a,) is terminated at 

 superior extremity by a point, and at the lower or incisive extremity 

 by five pretty strong teeth. The other piece is in the form of a re- 

 gular palpus, (Fig. 7j 6.) which issues from about the middle length 

 of the proper mandible, and consists of three joints, provided with 

 several setae, the first of which joints has, near its base, a very small 

 branchial plate, (Fig. 7 c,) terminated by five digitations. This 

 palpus is the second pair of feet of Jurine, the " barbillon/' of 

 Muller, the use of which, both agree, is to cause a current of water 

 towards the mouth, carrying with it the particles destined for the 

 insect's food. The first pair of jaws (Fig. 1. i. Fig. 8,) have for their 

 base a large square-shaped plate, (Fig. 8. a,) furnished at anterior 



* Straus says five. f Straus. 



