4.4.4, REPORT—1905. 
by the formation of a mortal neuro-epithelial host, which carried round the immortal 
germ cells, The differentiation of the host gave rise to the central nervous system 
and all tissues connected with it. The differentiation of the free living germ cells 
gave rise to the ‘archzocytes, as Minchin calls them, from which arose the mesen- 
chymatous tissues. This conception of the manner in which the body is built up 
puts the central nervous system in its right place, as the main factor in the forma- 
tion of the individual or host from the embryological point of view, just as it is the 
main factor in the development from the phylogenetic point of view. Finally, as 
pointed out by the author in his last paper in the ‘Journal of Anatomy and Phy- 
siology,’ vol. xxxix. p. 371, the manner in which the neural canal of the vertebrate 
is formed is on this theory the necessary consequence of the disuse of the ol éali- 
mentary canal of the arthropod ancestor. 
3. On the Growing-point in the Vertebrata, 
By Professor J. CLevann, M.D., F.R.S. 
It is well known that the medullary folds appear in close connection with the 
rimitive streak or blastopore, and that the parts concerned with the cranium and 
its contents are the first to appear, while both the mesoblastic somites and spinal 
nerves appear in succession, each metamere behind that which is immediately 
proserial to it. It follows, therefore, that it is from the short space between the 
medullary folds and blastopore that new metameres of the neuro-muscular system 
are formed, and there is no reasou to doubt that the visceral system is extended 
in the same manner. 
The nucleated corpuscles of this region furnish, therefore, the parents of the 
corpuscles of which the successive metameres of the trunk are composed, and 
they do so by giving off successive series of corpuscles which belong each to a 
particular metamere. This is precisely comparable with the early development of 
Aurelia, in which successive individuals appear each between those previously 
formed and the main or permanent part of the strobilus. It is just as in Aureliz, 
future separate individuals are given off successively from a corpuscular mass, the 
parent of the whole series. 
The only difference between these young Aurelie and the metameres of a 
vertebrate is that each becomes in the long run completely free from all the 
others. This makes it clear that the metamerism of the vertebrata, and indeed 
all metamerism, is of the nature of incomplete reproduction. In the head the 
metamerism is less complete than in the trunk, but the growth of successive parts 
is distinctly in the face proserial—that is to say, from behind forwards to the 
extremity of the nose and intermaxillary region. Thus the axial structure of the 
vertebrate animal takes place in two directions from a starting-point at the back 
of the head; and it may not be amiss to recollect that the vital node of Fleurens 
is situate in the neighbourhood of this starting-point, and also that in the higher 
divisions of the vegetable kingdom we have, in like manner, the plumule and 
radicle taking opposite directions from a common starting-point. 
