Miscellaneous. 495 
constant in the same species to admit of a comparison with those 
which I have just described in the shells of the living Nautilus.— 
Comptes Rendus, t. exx. no, 25 (June 24, 1895), pp. 1481-1434. 
On the Structure of the Ectoderm and Nervous System in Parasitic 
Platyhelminthes (T'rematodes und Cestodes). By Lton Jamuus. 
The results of my investigations upon the organization and deve- 
lopment of Nemathelminthes, which I have recently published, 
contain a detailed study of the ectoderm in these animals. The 
layer in question is constituted at its first appearance by a con- 
tinuous epithelium, the superficial growth of which slackens at an 
early period. Stretchings result from this fact, and consequently a 
more and more complete dissociation of the entire Jayer. The cells 
preserve their epithelial character or become transformed into nerve- 
elements, fibrils, and granulations. The nerve-elements are differen- 
tiated on the spot. The fibrils result from the elongation, accom- 
panied by a special transformation of the epithelial elements; they 
occupy the spaces left by the non-multiplication or cessation of 
growth of the cells of the primitive epithelium. The granules are 
due to the breaking-up of the fibrils. These different elements 
appear in varying proportions, according aS one examines the 
successive stages of the same individual or of different individuals ; 
they form a single and unique tissue, in which the nerve-elements 
remain scattered; the latter constitute, by their accumulation at 
various points of the body, the nervous regions of authors. 
These investigations, extended to the Platyhelminthes, have 
enabled me to determine that the ectoderm of the latter exhibits in 
its structure numerous points of resemblance to its homologue in 
the Nemathelminthes. We find in both cases epithelial cells, nerve- 
cells, fibrils, and granulations. Certain authors have described a 
layer applied to the cuticle; on account of its appearance they have 
ealled it granular ; but by the greater number of them it has been 
assigned to the mesoderm. This layer really corresponds to the 
ectoderm, transformed by processes similar to those which I have 
described in the case of the Nemathelminthes. 
My investigations have been made upon a Trematode, Distoma 
hepaticum, and upon two Cestodes, Tenia solium and Tenia inermis. 
The continuous descriptions of the nervous system of these animals 
are not such as to enable us to understand its relations to the rest 
of the ectoderm. Authors have constantly sought to isolate it and 
to give it definite and precise contours. The regularly increasing 
complications which they have described in its structure, in propor- 
tion as fresh nervous points were recognized, have led us to imagine 
the existence of a complex framework capable of uniting all the 
nervous elements distributed in the bodies of these animals. In 
Ann. & Mag. N. Hist. Ser. 6. Vol. xvi. 35 
