HABITS OF CRYPTOBRANCHUS ALLEGHENIENSIS. 35 



The yolk sac is greatly reduced, and in some specimens the 

 abdomen presents a shrunken appearance. The vitelline vein is 

 no longer visible. The larvae seize small pieces of beef offered 

 to them, but do not swallow them. 



Six Months' Larva. — Larvae six months after hatching meas- 

 ure about 40 mm. From the third to the sixth month the increase 

 in length is very slight, but the larva becomes much stouter in 

 structure. 



After the fifth month the larvae not only seize small pieces of 

 raw beef moved along a little to one side of the head, but, to a 

 limited extent, swallow and retain these morsels. The presence 

 of feces in the water indicates that some of the meat is digested. 



In larvae of this age fixed in Tellyesnicky's fluid and preserved 

 in alcohol, the lateral line organs are quite conspicuous ; their 

 distribution can readily be made out with the naked eye. 



Neither the larvae of this nor of earlier stages have been ob- 

 served to come to the surface for air. 



The course of larval development described above may be 

 somewhat slower under natural conditions on account of lower 

 temperature. During the period under consideration the tem- 

 perature of the aquaria ranged from 13 to 9 C, while that of 

 the stream from which the specimens came ranged from io° to 

 5° C. It is very probable that the larvae hibernate in the nest, 

 and perhaps do not emerge until late in the following spring. 

 I have found clusters of 35 mm. Necturus larvae late in August, 

 occupying what was apparently their original nest. 



At the time of writing a considerable number of larvae are 

 being kept alive in the laboratory, and it is hoped that some of 

 them may be reared to the adult condition. 



B. Later Stages Studied in the Field. 



During August of the past summer search was made for larvae 

 in their natural environment. A few larvae were found beneath 

 small flat stones in running water only three or four inches deep. 



The Year-old L^arva. — The smallest specimens obtained (see 

 Fig. 12) were about 7 cm. long. Four specimens were found 

 measuring as follows ; 6.4 cm., 6.8 cm., 7.0 cm., 7.3 cm. These 

 were presumably hatched during the preceding autumn. The ex- 



