THE REACTION TO LIGHT OF THE DECAPITATED 

 YOUNG NECTURUS. 



BY 



ALBERT C. EYCLESHYMER. 



{From the Anatomical Laboratory of St. Louis University.) 



During the summer of 1904 a large number of young Necturi 

 (15-18 mm.) were decapitated by pinching with fine forceps. 

 The heads were cut off, at sHghtly different levels, at about the 

 exit of the common trunk of the seventh and eighth nerves. 

 Although the percentage of fatalities ran high, many of the larvae 

 lived until the yolk was absorbed, usually about three months. 

 The larvas used in the following experiments were decapitated on 

 July 10 and in early September they had grown to a length of 30 

 mm. 



That the young and old Necturi are negatively phototropic is a 

 matterof everyday observation both in thenaturalenvironment and 

 in the aquarium. 



In testing the effects of various kinds of light on the normal and 

 decapitated larvae they were placed in a small glass aquarium about 

 60 cm. long, 30 cm. deep and 25 cm. wide. One-half of this 

 aquarmm was then painted black and the top covered with a 

 black board. The larvae, both normal and decapitated, were 

 then subjected to sunlight of varying degrees of intensity. The 

 rays were condensed by a hand glass and by concave mirrors, and 

 were also passed through ground glass. The light of the room was 

 controlled by an opaque curtain so that varying degrees of inten- 

 sity could be obtained. 



In order to test the effects of artificial light, the normal and 

 decapitated larvae were taken into a photographic dark-room and 

 the aquarium was placed in such a position that a sixteen candle- 

 power electric light illuminated one-half of the aquarium. In the 

 same manner one-half of the aquarium was exposed to the fight 

 from an arc lamp. Further experiments were made by controlling 

 these lights with condensers and mirrors. In all cases both the 



