ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
293 
according to the habitat of the fish, a fact which probably depends upon 
the distribution of the intermediate hosts. There is an antagonism 
between different kinds of parasites, e. g. between Distomum and Echino - 
rhynchus ; and the number which one host can sustain seems to be limited. 
Experiments, like those made by Bunge, show that entoparasites require 
only a minimum oxygen supply. Iu the second part of his paper, 
Herr Hausmann describes a few new and rare species. 
Entozoic Tuberculous New Formations.* — Dr. Y. Diamare describes 
certain appearances in the internal organs of Thalassochelys caretta which 
are due to the presence of the ova of a small Distomum, Mesogonimus 
constrictus. The subserous tissue is studded all over with miliary no- 
dules attached to the blood-vessels of the gastric and intestinal perito- 
neum. A closer examination shows that an egg occupies the centre of the 
nodule, the ovum or its remains being surrounded by a zone of giant- 
cells, and the whole included in a fibrous investment. 
Two Forms of Distomum cygnoides.f — According to Dr. R. R. 
Bensley, it would seem that under the specific name cyynoides , Pagen- 
stecherand Loossliave confused two forms of Distomum. One form pos- 
sesses an ovary divided into several lobes, nine testes, of which five are 
on the same side of the body as the ovary, four on the opposite side, and 
a vitellogen subdivided into several small lobules. The other possesses 
an undivided reniform ovary, two testes, and a much simpler vitellogen. 
It also attains a greater size, and is provided with a relatively smaller 
ventral sucker. 
Eyes of Turbellaria and other Flat Worms.:} — Dr. R. Hesse finds 
great dissimilarity of structure even within narrow range ; thus the eye 
of Planaria torva , which is taken as a starting point, is almost as 
different from the eye of Euplanarians as from that of Polyclads and 
Nemertines. In all cases, however, the eye is composed of sensory cells, 
which on part of their course are surrounded by a pigment cup, and are 
at this region specially modified for the perception of light. Thus the 
end towards the cup may bear fine filaments or fibrillar rods. These 
optic cells are always so disposed that the sensitive ends are turned ctwaij 
from the entrant rays of light. The differences between the various types 
depend mainly on the number and modification of the optic cells. In 
the case of the simplest eyes with one optic cell or with only a few, no 
power of image -forming can be thought of as possible. Quantitative 
and qualitative differences of illumination may, however, be perceived. 
Even in the eyes of Dendroccelum and Eujplanaria image-forming is not 
probable ; for, owing to the arrangement of the optic elements, a ray must 
in many cases meet several elements. In Polyclads only do the rods lie 
in one plane, but they are not separated by pigment sheaths, and image- 
forming is very improbable. The author describes numerous types in 
detail. 
Remarkable new Planarian.§ — Dr. A. Willey found at Lifu a new 
type of Planarian, which he calls Heteroplana Newtoni. It presents 
* Centralbl. f. Bakt. u. Par., l te Abt., xxi. (1897) pp. 459-65. 
t Tom. cit., pp. 326-31 (1 pi.). 
X Zeitschr. f. wiss. Zool., lxii. (1897) pp. 527-82 (2 pis , 3 figs.). 
• § Quart. Joum. Micr. Sci., xl. (1897) pp. 203-5 (1 fi<r.). 
1897 
X 
