203 Eelation of Nervous System to the Developing Musculature 



fortunately it is possible to see immediately after making the cut 

 just what has been removed, for in successful cases, on examining the 

 wound surface with a lens, the notochord stands out as a distinct rod 

 with the myotomes arranged alongside (Fig. -i). The operation may 

 also be done successfully with a sharp, fine pair of scissors. In some 

 experiments the thin strip of tissue containing the spinal cord was cut 

 off entirely (Fig. 2) ; in others it was left hanging at its anterior end, 

 but prevented from healing again to the nu^in portion of the embryo 

 (Fig. 4). 



The embryos were kept after the operation in ordinary tap water or 

 placed for a day or two in dilute salt solution, which insures a somewhat 

 more rapid and perfect healing of the wound. This usually takes place, 

 however, without difficulty in any case and even in two or three hours 

 the wound is usually closed. As a control to the study of the further 

 development, normal embryos of the same age were kept side by side with 

 those which had been operated upon, and specimens of each were pre- 

 served from time to time for the purpose of studying their internal devel- 

 opment. 



As regards their external form, the embryos develop in the best in- 

 stances normally except for the defect produced directly by the operation. 



Their development is, 

 however, considerably re- 

 tarded, not only in the re- 

 ta> \ gion 'of the trunk and 

 tail but also in the head 

 where the nervous system 

 was left intact. The in- 



FiG. 3. Palustris lai"\a six days after f'Xfisii 111 of the t • i n txs j? 



spinal cord as in Fig. 2. X 9^i. dividuals ditter Irom one 



another considerably, ow- 

 ing, no doubt, to slight differences in the amount of tissue originally 

 cut away. In the most favorable cases ( Fig. 3 ) the tail is almost straight 

 and shows only a lack of the dorsal part of the axis and the dorsal fin, but 

 as a general rule the tail acquires a marked dorsal bend (Fig. 6), espe- 

 cially in sylvatica larvi'e. In other cases, when the notochord has been 

 injured, considerably greater deformity arises; this manifests itself in 

 the crumpling and shortening of the tail, or sometimes even in its almost 

 complete atrophy. 



One rather remarkable feature, which shows itself constantly, is the 

 presence of a small portion of the dorsal fin at the tip of the tail (Figs. 

 3 and fi). Microscopic examination shows that a small portion of the 

 medullary tube is also present at that point. The development of these 



