6 Dr. W. Salensky on Hackel’s Gastreea Theory. 
we may suppose such a stage to occur in Strongylus jfilaria 
and Cucullanus. In all Nematoda an embryo consisting of 
two layers is formed after the conclusion of the process of seg- 
mentation, Irom the outer layer is formed the body-wall, 
from the inner one the intestine. The production of the in- 
testinal cavity occurs at the time of the formation of the body- 
cavity. 
The researches of Kowalevsky on the embryology of Sagitta* 
establish beyond doubt that in the embryology of this worm 
we may admit a Gastrula-stage. 
The statements of Hiickel that a Gastrula-stage occurs in 
the Bryozoa do not agree with the known investigations. 
From the researches of Nitsche+, Claparédef, and Mecznikoff 
we know that at any rate in the bicellarie (Bugula) no 
stomachal cavity is formed in the larva. As to the embryonic 
development of the Cyphonautes-like larvee, which, as is well- 
known, possess an intestinal canal, we have no information. 
In the postembryonic developmental history of the Bryozoa, 
which has been better investigated than their embryonic de- 
velopment, we find no state which has any resemblance to the 
Gastrula-stage. It is well known that here the intestinal 
canal (polypide) is developed in a very different manner from 
other animals. 
In the class Gephyrea, if Phoronis is to be referred to it, a 
Gastrula-stage occurs in that worm. 
Hiickel’s statement that Hwaxes in its ontogeny passes 
through a G'astrvula-stage, is decidedly not correct. The re- 
markable investigations of Kowalevsky, upon which Hiickel 
depends, best prove this. From the embryology of the Oli- 
gocheta we learn that cases may occur in which, in the same 
group of animals, one animal passes through a decided Gas- 
trula-stage in its ontogeny, while another does not. ‘This 
fact alone sufficiently proves that, in the demonstration of the 
Gastrea theory, we can by no means be contented with a few 
representatives of the animal types. The two Oligocheta 
which Kowalevsky has selected as the subject of his researches, 
Euaxes and Lumbricus (the ontogeny of Tudbifex is like that 
of Huawxes) show very essential differences in their first em- 
bryonic stages. In Huaves the segmentation takes place in 
the way which is so characteristic of some Vermes and Mol- 
lusea, After the first cell-division four large spheres of seg- 
mentation are formed, upon which a great quantity of smaller 
* “Embryologische Studien an Wiirmern und Arthropoden,” in Mém. 
de Acad. Imp. de St. Pétersh. tome xvi. 
+ Zeitschr. fiir wiss. Zool. Bd. xx. 
{ Ibid. Bd. xxi, 
