180 
MR. F. M. BALFOUR ON THE DEVELOPMENT OF 
The presence of this connective-tissue, in addition to the nerve-rudiments, removes 
the possibility of erroneous interpretations in the previous stages of the Pristiurus- 
embryo. 
It might be urged that the two masses which I have called nerve-rudiments are 
nothing else than mesoblastic connective-tissue commencing to develop around the 
neural canal, and that the appearance of attachment to the neural canal which they 
present is due to bad preparation or imperfect observation. The sections of both this 
and the last Torpedo-embryo which I have been describing clearly prove that this is 
not the case. We have, in fact, in the same sections the developing connective-tissue 
as well as the nerve-rudiments, and at a time when the latter still retains its primitive 
attachment to the neural canal. The anterior root (fig. D b, ar) is still a distinct conical 
prominence, but somewhat larger than in the previously described embryo ; it is com- 
posed of several cells, and the cells of the spinal cord in its neighbourhood converge 
towards its point of origin. 
In a Torpedo-embryo (Plate 16. fig. Dc) somewhat older than the one last described, 
though again derived from the oviduct of the same female, both the anterior and the 
posterior rudiments have made considerable steps in development. 
In sections taken from the hinder part of the body I found that the posterior rudi- 
ments nearly agreed in size with those in fig. D b. 
It is, however, still less easy than there to trace the junction of the posterior rudi- 
ments with the spinal cord, and the upper ends of the rudiments of the two sides do 
not nearly meet. 
In a considerable series of sections I failed to find any case in which I could be abso- 
lutely certain that a junction between the nerve and the spinal cord was effected; and 
it is possible that in course of the change of position which this junction undergoes 
there may be for a short period a break of continuity between the nerve and the cord. 
This, however, I do not think probable. But if it takes place at all, it takes place 
before the nerve becomes functionally active, and so cannot be looked upon as possessing 
any physiological significance. 
The rudiment of the posterior nerve in the hinder portion of the body is still approxi- 
mately homogeneous, and no distinction of parts can be found in it. 
In the same region of the body the anterior rudiment retains nearly the same condi- 
tion as in the previous stage, though it has somewhat increased in size. 
In the sections taken from the anterior part of the same embryo the posterior rudi- 
ment has both grown in size and also commenced to undergo histological changes by 
which it has become divided into a root, a ganglion, and a nerve. 
The root (fig. D c, pr) consists of small round cells which lie close to the spinal 
cord, and ends dorsally in a rounded extremity. 
The ganglion ( g ) consists of larger and more elongated cells, and forms an oval mass 
enclosed on the outside by the downward continuation of the root, having its inner side 
nearly in contact with the spinal cord. 
