DEVELOPMENT OF ELASMOBRANCH FISHES. 



my oldest Torpedo embryo (just younger than K) there is no 

 trace of it present. In a Torpedo embryo of stage I the sub- 

 notochordal rod of the trunk terminated anteriorly by uniting 

 with the wall of the throat. The junction was effected by a 

 narrow pedicle, so that the rod appeared mushroom-shaped in 

 section, the stalk representing the pedicle of attachment. 



On the formation of the dorsal aorta, the subnotochordal rod 

 becomes separated from the wall of the gut and the aorta in- 

 terposed between the two. 



The subnotochordal rod attains its fullest development 

 during stage K. Anteriorly it terminates at a point well in 

 front of the ear, though a little behind the end of the noto- 

 chord ; posteriorly it extends very nearly to the extremity of 

 the tail and is almost co-extensive with the postanal section of 

 the alimentary tract, though it does not quite reach so far back 

 as the caudal vesicle (PI. 18, fig. 6bx). In stage L it is still 

 fairly large in the tail, though it has begun to atrophy an- 

 teriorly. We may therefore conclude that its atrophy, like its 

 development, takes place from before backwards. In the suc- 

 ceeding stages I have failed to find any trace of it, and con- 

 clude, as does Professor Semper, that it disappears completely. 



Gotte 1 is of opinion that the subnotochordal rod is con- 

 verted into the dorsal lymphatic trunk, and regards it as the 

 anterior continuation of the postanal gut, which he believes to 

 be also converted into a lymphatic trunk. My observations 

 afford no support to these views, and the fact already men- 

 tioned, that the subnotochordal rod is nearly co-extensive with 

 the postanal section of the gut, renders it improbable that both 

 these structures are connected with the lymphatic system. 



1 Entwicklungsgeschichte d. Unke, p. 775. 



