650 AGNES I. M. ELLIOT. 



(see fig. 4) associated with it, and the third myotome is 

 accompanied by a well-developed ganglion. 



In fig. 2 the distinction betAveen the first ganglionated 

 root of the vagus and the succeeding group of roots is well 

 marked. The more posterior roots have formed a common 

 trunk which is running forward to join the first root. There 

 is a rudimentary ganglion to the second myotome, but it is 

 not cut in either fig. 2 or fig. 3, and the ganglion of the 

 third myotome is only just shaved in the section shown in 

 fig. 3. Neither in this nor in any other section is there any 

 trace of a ganglion in connection with the first myotome, 

 nor with the mesoblast lying in front of the first myotome. 

 If the segments are counted back to the cloaca (the only 

 approximately fixed point, as the limbs have not begun to 

 develop) they are found to be eleven in number. 



Fig. 4 is a horizontal section through another tadpole of 

 about the same age, showing all the anterior myotomes and 

 associated ganglia. The first myotome is small, and has no 

 trace of a ganglion, the second has on the left side a rudi- 

 mentary ganglion associated with it ; each of the other myo- 

 tomes corresponds with a well-developed ganglion. The vagus 

 roots on the right side arc seen crossing outwards over the 

 first myotome. In fig. 4a we have the rudimentary ganglion 

 of myotome 2 enlarged. In fig. 45 we have a typical spinal 

 ganglion from the same tadpole enlarged to show the contrast. 



Fig. 5 is a horizontal section through a much older tadpole, 

 about 13 millimetres long, in which the cartilaginous dorsal 

 neural arches are developed. The first neural arch lies at a, 

 on the myoseptum between the first and second myotomes 

 now present. In front of this, however, are two small carti- 

 lages h and c, which look serially homologous with the neural 

 arches, and lie just behind the ganglion of the vagus. In 

 more ventral sections they may be seen to fuse with cartilage 

 continuous with the otic capsule. These, I believe, represent 

 two neural arches — are, iu fact, homologous with the pre- 

 occipital and occipital arches which Miss Piatt found in 

 Necturus. The first myotome now present has a distinct 



