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THE AMERICAN NATURALIST [Vol. XLT 



The accompanying camera sketches from specimens hardened 

 in Worcester's liquid show the generally imperfect state of the 

 appendages of the first larva, which lived for a few days an inert 

 embryo-like existence fastened to the mother and not eating but 

 only rapidly aerating and circulating its blood as the yolk was 

 being transformed. The first antenna, figure S, has only four 

 segments in its exopodite and iti its (Midojxxlite and agrees with 

 most of the other appendages in being devoid of set;e. This bare- 

 ness of the appendages of tiie first larval stage was first pointed 

 out in the English Astacus by Huxley and seems connnon to all 

 crayfish larvae in their first stage. In place of set* there are but a 

 few spinules at the tips of the first antenna and on the basal seg- 

 ment there is a small ear-pit; but as yet the entire appendage 

 would seem of no use as a sense organ. 



The second antenna, figure 9, has only 24 segments in the slender 

 part of its filament, beyond the three large broad segments, and the 

 exopodite scale bears a blunt process and a row of few, sharp 

 spines. The tubercle upon which the nephridial canal opens is, 

 as in all young crayfish, proportionally very large. 



The mandible, figure 10, has a smooth edge with no teeth and 

 is probably not used. The first maxilla also, figure 11, is very 

 simple and probably of no use. 



The second maxilla, on the other hand, figure 12, bears the 

 large scaphognathite which is very active in removing water from 

 the gill chamber. The seta? along the edges of tlie scaphognathite, 

 though represented in the figure as smooth, were in reality, under 

 2. I)., set with five side l)ranches so that in this only activelv mov- 

 ing appendage the setje are present as plumes that would seem to 

 be of use in striking against the water and m making the ap[)endage 

 fit more closeK nito tin p,.^,^. h idm- out of tlu gill (hambei 



The three maNihipcd-. li-nro i:;. I I. lo. are stranuvlv lacking 



