84 CASWELL GRAVE 



ends, possibly having a distribution to muscle fibers which are 

 in this region rather richly developed. The origin and course 

 of this nerve are shown in figures C, D, and 3. Its function 

 during the free-swimming period of the larva is not evident and, 

 on account of the rigidity and immobility of the body, is diffi- 

 cult to conceive. Non-striated muscle fibers are present in 

 considerable number in the mesenchyme layer just beneath the 

 body wall in the region into which the nerve can be traced. 

 These muscle fibers take a general course from the region of the 

 endostyle obliquely forward to the ventral side of the body. 

 Slow writhing contractions of the entire body are very evident 

 at the close of the free-swimming period when metamorphic 

 changes have set in, and it is possible the neuromuscular appara- 

 tus under consideration first comes into function at this time. 

 Salensky's conception of the visceral ganglion as the reflex 

 center or brain of the larva seems to be substantiated by phys- 

 iological as well as by structural data. My observations on 

 the reactions of the Amaroucium tadpole (Grave, '20 b) indicate 

 that the tadpole orients with reference both to light, by means 

 of reflexes originating in the eye, and to gravity, by means of 

 reflexes originating in the static organ. It was found that 

 the normal response to gravity during the latter part of the 

 free-swimming period was greatly modified in the presence of 

 unusual stimulation by light. The visceral ganglion must be 

 the coordinating center for these diverse reflexes. 



THE NERVE CORD 



Due to a permanent twist of the tail 90° to the left, the nerve 

 cord occupies a position on the left side of the notocord in the 

 space between the projecting edges of the dorsal and ventral 

 muscle bands (figs. C, 3, 8, and 10). Near the anterior end of 

 the notocord the nerve cord bends abruptly upward and slightly 

 to the right to join the ventral end of the visceral ganglion. A 

 definite neural canal is present throughout its length. Small 

 nuclei are present here and there in the thin wall of the cord, 

 but none were found that have the characteristics of nerve cells 

 (figs. 3, 8, and 10). The cord tapers toward the end of the tail, 



