Eoss Granville Harrison ' 203 



structiire.s, lyinjj: dorsal to the axis of tlio tail assumes in some instances 

 considerable proportions. When it is considered that everything dorsal 

 to the notochord was removed by the operation, it is clear that this por- 

 tion of the medullary tube must have regenerated in an anterior direction 

 from the walls of the neurenteric canal. 



The series of drawings (Figs. 4-G), made from one embryo at different 

 stages of its development, gives an idea of the development of tlie indi- 

 vidual. The first cut (Fig. 4) shows the em- 

 bryo just after the operation. In this case the 

 strip containing tlie spinal cord was left hang- 

 ing to the head. The second stage (Fig. 5) is 

 one day older. Here the tail shows a distinct 

 dorsal flexure, due probably to the fact that the 

 distal end of the notochord had been cut out, "~— -— - 



and considerable growth had taken place before i J^*^edittef/^'after cuSg 

 the complete regeneration of the notochord oc- ^^^ spinal cord, x 91^. 

 curred. The cut edge of the small dorsal strip 



has also healed over and is beginning to coil up in a horizontal plane. Six 

 days after the operation the larva appeared as in Fig. (i. The tail is 

 normally expanded, but still shows the marked dorsal flexure. The small 

 strip of tissue resting on the back has coiled itself up ; the dorsal fin 

 belonging to it is well developed. The larva is oedematous and the lymph 

 sinuses are much dilated. This condition is not uncommon in such 

 specimens. Examined more carefully under moderate powers of magnifi- 

 cation, the arrangement of the muscle 



— ^ ' „ ,,^^ ^ plates in the tail is found normal. The 



^"^^SiT^ ^"^^ individual segments are Y-shaped as 

 I usual, although the dorsal arm is short- 



\ ened by the amount removed by the 



operation. The primary abdominal mus- 

 "^ -" cle is also present and extends anteriorly 



Fig .5 Same specimen as in Fig 4 from the mvotomes at the base of the 

 one day after the operation. X 9^.. ^^-^^ spreading out into a thin sheet in 



the abdominal walls. 

 The physiological differences between the embryos experimented upon 

 and the normal ones are marked. While the latter soon acquire the power 

 of movement and respond readily to stimuli, the former remain motion- 

 less even when stimulated strongly, except for the movements in several 

 anterior myotomes where the cord had been left in connection with the 

 body. In certain cases the tail exhibited independent twitching move- 

 ments; in these cases a considerable stretch of the spinal cord was found 



