of the Animal Kingdom. 329 
exception of the Nemertina) and the group of the Annelida. 
Of these latter, however, the Polychaeta differ essentially in 
their mode of development from the Oligocheta, and, more- 
over, as is well known, there are many other forms, such as 
the Nematoda, Acanthocephala, Gephyrea, Cheetopoda, Entero- 
pneusta, and Rotatoria, which differ not inconsiderably, in 
many respects, not only from the above-mentioned Annelida 
and Scolecida, but also from one another. 
From the consideration of all these facts, from the stand- 
point of phylogenesis, in accordance with the present state of 
science, only one thing can be accepted as established, namely, 
that the Helminthozoa form on the genealogical tree of the 
animal kingdom, a knot, which ts at present not quite untiable, 
from which probably all the other higher stems have branched 
off (see the Table, p. 534); and, consequently, there is no 
doubt that the main stem of the Helminthozoa was of the 
greatest importance in the origin and descendence of the 
higher types. 
From the results of recent. embryological investigations it 
is sufficiently clear that the embryos, as well as the free- 
swimming ciliated larvee, of different Vermes more or less 
resemble the larvee of the Echinodermata, Bryozoa, Brachio- 
poda, many Mollusca, and the Provertebrata (‘T'unicata and 
Leptocardii). From the remarkable similarity of the con- 
ditions of development of these animals it is further to be 
assumed that these might all have originated by the process 
of natural selection from one or more simple, vermitorm, 
primitive forms. Nevertheless we must freely admit that the 
known facts of embryology, as well as all the hypotheses 
built upon these facts, by no means suffice for the final deci- 
sion of the question, From what special primitive form have 
the Mollusca, Bryozoa, and Brachiopoda, the Arthropoda and 
the Provertebrata been phylogenetically developed? Both 
in amount and in importance the facts at present known are 
only capable of proving this much: that the great stem of 
the Helminthozoa very probably forms the starting-point for 
the higher animal-stems of the Echinodermata, Arthropoda, 
Malacozoa, and Chordovertebrata. 
Further, as regards the opinion of Prof. Semper and other 
zoologists, according to which the Annelida are specially 
adopted as the ancestors of the Vertebrata, I may here be 
permitted only to remark that the facts cited for the esta- 
blishment of this opinion (the segmental organs or primitive 
kidneys) do not, in my estimation, suffice to demonstra‘e in- 
dubitably that the Annelida are in reality more nearly allied 
Ann. & Mag. N. Hist. Ser. 5. Vol. xii. 22 
