DEVELOPMENT OF THE OAPE SPECIES OF PERIPATUS. 205 
tissue cells, cartilage cells, epithelial cells, &. And not only 
may the cells of one tissue be continuous with each other, but 
they may also be continuous with the cells of other tissues. 
For instance, I may refer to Fraipont’s (2) work on the nervous 
system of the Archiannelida. He describes an intermuscular 
nervous plexus which is continuous with the muscle-cells and 
with the surface epithelial cells (2, Pl. 13, figs. 11, 16). 
Instances of this kind might be multiplied from recorded 
observations, and are being multiplied day by day by histolo- 
gical observers to such an extent, that we are almost, if not 
quite, justified in regarding the body of an adult animal as a 
syncytium. It is true that the cells of the blood and lymph, 
and the ripe generative cells, are completely isolated. But the 
former, in their first stages of growth, form part of the syncy- 
tium ; as in all probability do the latter also.! 
This continuity, which for a priori reasons we should 
expect, has hitherto been regarded as a fact of little morpholo- 
gical importance and relegated to the category of secondary 
features. The ovum, it is said, segments into completely 
isolated cells; and the connection between these is a secondary 
feature acquired late in development. It has always been con- 
sidered that the first stage in the evolution of the Metazoa 
was a colonial Protozoon, i. e. a mass of perfectly isolated uni- 
cellular organisms derived by complete division from a single 
cell. 
Now, while I do not wish to exalt the facts of the cleavage 
and early development of Peripatus above recorded to a posi- 
tion of undue importance, or to maintain that of themselves 
they are sufficient to destroy this conception of the origin and 
structure of a Metazoon, I think I am justified in pointing 
out that if they are found to have a general application, our 
ideas on these subjects and others connected with them will 
have to undergo a considerable modification. 
The ancestral Metazoon will no longer be looked upon as a 
colonial Protozoon, but rather as having the nature of a multi- 
1 T may refer in this connection to the processes of the follicular cells which 
perforate the zona of a mammalian ovum, 
VOL, XXVI,—NEW SER, P 
