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THE AMERICAN NATURALIST [Vol. XLI 



Camera lucida sketches of the first larva of C. diogenes showed 

 it larger than even the second stage of C. clarkii but in simplicity 

 and proportions essentially like the first stage. As usual in hatch- 

 ing crayfish the appendages were almost all bare of setse; the eyes 

 were nearly sessile; the rostrum a small triangle close to the body 

 and between the eyes. The yolk far forward in the head-thorax 

 distended that region and left the region for the gills and pereiopods 

 of less extent. 



In the first antennae there were four segments in the larger, club- 

 like exopodite and also in the slender, smaller endopodite and 

 there were no sensory setse. 



The second antennse were carried curved backward and down- 

 ward but not close against the thorax as in C. affinis and each had 

 only spines upon its scale and 35 segments on the slender part of 

 the filament. 



The mandible had no teeth but its edge was very slightly waved 

 where the epidermal cells seemed about to secrete slight thicken- 

 ings. 



The scaphognathite used as a baling organ also was exceptional 

 amongst the appendages in bearing plumose setae which formed 

 a row along the edge and were longer and more easily seen than in 

 C. clarkii. 



The gills were larger and with more side filaments than in C. 

 clarkii but were suddenly reduced upon the fourth pereiopod so 

 that the anterior arthrobranch had but a few filaments and the 

 posterior none. On the last thoracic somite there were no gills, 

 as is the case in all the young of Cambarus thus far studied. 



The four pairs of pleopods had the endopodites slightly longer 

 than the exopodites and the entire appendage was very much 

 longer than in C. clarkii and with evident spines on both tips. 



The telson with its enclosed pleopods was very much like that 

 of C. clarkii and bore on its posterior edge the same kind of spines, 

 about 14 on each side, six of which wore specialised gland ducts 

 archc.l over and ioincd u^ivtUvv and l.<.un.] to the tfl^..n strino- 



stage and a day befon 

 extended from their gla 



