516 WILLIAM BATESON. 
tudinal fibres of the “ punktsubstanz,” or may pass directly 
through this as motor fibres into the muscles. 
The next point relates to the question as to the intervention of 
some third cell in their course functioning as a ganglion cell. In 
B. Robinii, in which the examination of this subject is most 
complete, as stated above, the occurrence of such cells could 
not be shown; but this is, of course, by no means conclusive 
in face of the antecedent probability of their occurrence. The 
“ punktsubstanz,” then, would mainly consist of afferent fibres 
passing to the central nervous system, and the motor fibres 
probably pass directly through it. As will be shown in the 
next paragraph its distribution agrees with this view. 
In the account of the general development the central 
nervous system was shown to have arisen chiefly by a solid 
delamination from the skin, added to which its anterior, and 
to some degree its posterior, ends are being continually 
invaginated as growth continues, so that each end is tubular. 
This tubular form results not so much from the longitudinal 
closure of a tube as from a forward and backward growth of 
skin at the extremities of the delaminated cord. Soon after 
delamination histological differentiation occurred between the 
upper cellular and lower fibrous parts of the cord. While 
tiiis was proceeding (2, g.s.) fibrous tissue was deposited to 
form the ventral cord at the point of this structure, which 
was most anterior (viz. the back of the collar). While this is 
proceeding the deposition of similar tissue in the region of the 
dorsal cord commences at the posterior attached end of the 
central nervous system. Next, the deposition of fibrous tissue 
extends itself forwards on to the proboscis, being first laid down 
in the dorsal middle line of the proboscis stalk (v. figs. 34 and 
35, pkt.). On the appearance of the atrial fold the ventral 
and dorsal cords become united by a fibrous ring in the inner 
angle of the fold. This ring, therefore, may be supposed to 
bring up the fibres from the ventral cord to the central 
nervous system, which it enters at its posterior end, together 
with the dorsal cord (v. diagram, fig. 65). 
The greatest concentration following upon these occurs in 
