494 Miscellaneous. 
reality the nervous system has no definite outlines; the regular 
arrangements, consisting of sharply defined rings and of divergent 
cords, which have been attributed to it, cannot be considered as an 
expression of facts. The apparatus is diffuse and united with the 
rest of the ectoderm. 
In Distoma hepaticum the nervous elements present in the various 
parts of the body appear especially numerous in the cephalic region 
and at the level of the genital sinus. Around the pharynx in 
particular we see them surrounding the passage and filling the 
rounded groove bounded by the external face of this organ and the 
inner surface of the cuticle enveloping the body. The special 
reagents show that this mass of nerve-elements, instead of having 
definite outlines, merges at its margins into the granular layer. 
The nerves of authors are nothing else than thickenings of this same 
tissue. It follows that Distoma hepaticum possesses, in place of a 
nervous system consisting of a principal centre (cerebral ganglia) 
and dependent parts, a fibro-cellular ectoderm in which nerve- 
elements exist at places, while these elements are especially developed 
in the regions in communication with the exterior, 7. e¢, mouth and 
genital sinus. 
The same state of things exists in the Cestodes which I have 
studied. Only the changes undergone by the ectodermal layer are 
perhaps easier to grasp because they appear at different stages in 
the same individual and according to the age of the segments. 
The history of the granular layer of the Platyhelminthes is the 
same in its general features as that of the ectoderm in the Nemat- 
helminthes. Authors have sought at the outset to isolate the 
nervous system by distinguishing in it centres and dependent parts ; 
this course tended to make of the apparatus of communication an 
autonomous whole, which it was necessary to delimit. The study 
of its relations to the ectoderm, which I hope to be able to complete, 
shows, on the contrary, its entire continuity with the latter, and 
even thereby obliterates the contours which determined it. 
This structure of the ectoderm, common to Platyhelminthes and 
Nemathelminthes, is to be connected with the presence in all these 
animals of a thick and resistant cuticle ; I have already insisted upon 
this point in my paper on the Nemathelminthes ; I believe that I am 
confronted with a histological structure, connected with the existence 
of an impermeable envelope, which almost suppresses or, in all cases, 
greatly modifies the relations of the ectoderm to the external 
medium *.—Comptes Rendus, t. cxxi. no. 5 (July 29, 1895), 
pp. 268-270. 
* This paper was prepared at the Natural History Laboratory of the 
Faculty of Sciences of Toulouse. 
