59 



The first pair of limbs (lig. s) I?; rohnsf, ob.scurely articulated, 

 ending in what appears to bo a blade like pair of scissors (bristle and 

 sheath, Dana); this pair ultimately bears at the extremities, in place of 

 bristle and sheath, perfect sucking-cnps for holding on to smooth 

 surfaces ; the second pair (a) is closely like that of the adult, the 

 hooks and conformation indicate that they are for progression and 

 firm attachment. The four succeeding pairs of natatory limbs are 

 made sufficiently clear by the cut (n', n\ n*, n*), except the differences 

 between the plumose fingers in this and the perfect animal; in the 

 adult these limbs all terminate in two such fingers ; in the larva there 

 appears to be three, close examination shows that they are but two 

 fingered, but that the lower finger is two jointed and undivided, while 

 the upper one is two jointed with a secondary finger at the articulation; 

 the lower finger of first natatory is three jointed, not plumose, ending 

 in spines. 



The abdomen (y) differs widely from that of the mature form ; 

 it is relatively small, ovated ; retuse- truncate in outline instead of 

 terminating in two long acute lobes ; besides on the posterior bordoi' 

 stand two rounded protuberences between which is the anal opening ; 

 they remind one of the abdomen of allied forms of Philloi)oda and 

 Oopepoda (Thorell). In the adult these bodies have worked up 

 to the bifurcation of this expanded i)]ate (except in .1. Lepidostei in 

 which they stand near the apex of the lobes) and remain small and 

 rudimentary : although rudimentary, they must not be despised, for 

 they not only point out the affinities of the Artjxdidae as above, but 

 determine, as well, the true nature of this "plate"; it is plainly the 

 abdomen morphologically, it is as plainly a respiratory organ physio- 

 logically to one who has attentively studied the character of the 

 circulation. It has been variously designated by authors. At t, in 

 the figure, are two small brown bodies which are evidently an indi- 

 cation of what are afterwards the receptacula seminis of the female 

 or the testes of the male, then situated near the base of the lobes. 



The degree of advancement reached by this species before quitting 

 the ovum is ([uite unexpected. If I had not removed and examined 

 many embryos, I should have suspected that these had suffered 

 several moults before being observed, but those removed exhibit all 

 the points of the one figured, so they certainly had not materially 

 changed, nor did they during two pbsequent days at the end of 

 which they died. As Dana figures the larval catostomi at hatching, it 

 has only the first pair of swinmiing legs, having for its organs of 



