328 Dr. T. Margé on the Classification 
tary canal, modified in the way just mentioned, with the name 
of Metentera. 
To the great main-branch of the Metentera belong, above 
all, in our opinion, the vermiform animals or Helminthozoa. 
According to all extant investigations, these animals form one 
of the oldest of the great stems or phyla of the whole genea- 
logical tree, most important from a phylogenetic point of 
view, and most interesting anatomically and embryologically. 
The group Helminthozoa embraces very many different 
forms, which, as regards both their structure and their mode 
of development, differ so much from each other that it can 
hardly be regarded as too bold an assertion to say that, in the 
whole animal kingdom, there is hardly another stem that 
would embrace such different and sometimes widely divergent 
modifications or classes. For this reason, also, it seems 
scarcely permissible to regard the Vermes as forming an 
equally unitary animal-type, as, for example, the Arthropoda, 
Echinodermata, Coelenterata, and other great groups. Thus, 
among other things, the Platyelmintha (with the sole ex- 
ception of the Nemertina) are distinguished not only by 
greater simplicity of organization, but also essentially by the 
absence of a true coeloma, from all other Vermes, and even 
from all Metentera. Nay, from this last-mentioned nega- 
tive character (the absence of a cceloma) they might quite 
logically be regarded as a special group of the Archentera. 
We must not forget, however, that the Platyelmintha which 
are destitute of a ceeloma (Turbellaria, Trematoda, and Ces- 
toda) are, on the other hand, nearly related to the Nemer- 
tina, and through these to the other groups of the same stem, 
all of which are furnished with a cceloma; also that the other 
groups of the Vermes deviate from one another in many 
respects, and sometimes considerably, especially when we 
take into account the segmentation of the ovum and the 
mode of formation of the cceloma. Chiefly for this reason we 
hold it necessary for the present still to regard the Platyel- 
mintha as united with the other groups of Vermesinthe common 
stem of the Helminthozoa, although, by many naturalists, 
attempts have already been made to divide this stem into 
several subordinate stems or subphyla. But if we consider 
how imperfect the knowledge still 1s that we possess as to the 
structure and development of the Vermes, we must regard all 
such attempts at the present day as premature. 
The results of the numerous investigations hitherto made 
seem only to prove one thing, namely, that the stem Vermes 
is perhaps very well divisible mto two or several divergent 
branches—the group of the Scolecida (Platyelmintha with the 
