108 Dr. F. Muller on the Metamorphoses of the Praivns. 



small ridges and tubercles. At the base of the tooth, towards the 

 masticatory surface, there are several stiff bristles, beset with 

 short spinules (fig. 7) . The upper jaws are destitute of palpi. This 

 appears to be a peculiarity in which all Zo'em agree with Insects, 

 and which is in this case doubly remarkable, because not only 

 does the perfect animal possess mandibular palpi, but even the 

 younger larvae have at this place biramose feet, from which the 

 mandibles are produced. 



In the lower jaws {maxilla, fig. 4 iv, y) we distinguish — 1. the 

 peduncle with projections on its inner side, which have almost the 

 appearance of joints, and are beset with strong bristles, partly 

 spiniform and partly toothed or plumose; 2. a multiarticulate 

 apical portion (inner branch ?), which bears longer and more 

 delicate bristles on its inside and at its apex ; and 3. a small, 

 elongated, lamelhform appendage (outer branch ; fouet, Milne- 

 Edwards, fig. 4 a a), on the margin of which are placed a few 

 delicate setae. In the first pair of maxillae (iv) the peduncle has 

 two long, and in the second pair (v) four shorter processes; 

 the apical portion has in the former three, and in the latter five 

 joints. 



The footjaws (vi, vii) or maxillipeds appear to assist but 

 little in locomotion. They consist of a thick peduncle (thickest 

 in the first pair), a long 4-5 -jointed inner branch, and a shorter 

 inarticulate outer branch. Besides the apical setae, there are 

 bristles of various lengths upon the inner margin of the peduncle 

 and of the inner branch, and also upon the outer margin of the 

 outer branch. The first pair is longer and more powerful than 

 the second. 



The two branches of the tail project, separated by a semicir- 

 cular notch, nearly at a right angle to each other ; they appear 

 to be rounded off at the apex, and twice acquire a new bristle on 

 their inner margin, so that the number of these rises first to 

 seven and then to eight on each branch. The oldest bristle 

 continues to be recognizable by its greater length (0'4 mill.) ; 

 the outermost bristle (the spine which is present even in the 

 youngest Nauplius) continues to be distinguishable from the rest 

 by its being smooth, whilst the others are rendered plumose by 

 short spinules and longer hairs. 



The alimentary canal presents no peculiarity ; the anus, which 

 is at first situated at the apex (PI. IV. fig. 3), afterwards moves 

 forward on the ventral surface nearly to the middle of the last 

 segment (fig. 6). The liver, of a yellowish colour, consists of 

 three pairs of wide tubes (one pair anterior and superior, one 

 pair lateral, and one pair posterior and inferior), and does not 

 differ in its structure ft-om that of other Zo'ets. 



The heart (fig. 3 h) occupies the usual position at the end of 



