Miscellaneous. 415 
larvee which become quickly transformed, larvee of delayed fixation, 
in which the dissepiments become sketched out even while the ver- 
miform stage persists. The most curious character of these larve 
consists in the structure of their integuments. No sclerites are as 
yet formed, but the ectoderm has become differentiated after the 
fashion of the Clavularie. The cells have pushed forth muscular 
processes. At the base of the pseudomesoderm a fibrous layer cor- 
responds to an annular muscular band. Very numerous primitive 
mesenteric folds have been formed; and the whole endoderm is asso- 
ciated with a layer of longitudinal muscular fibres. The transverse 
section of these larve is almost identical with that of an Actinia.— 
Comptes Rendus, September 25, 1882, p. 562. 
On the Histological Structure of the Digestive Tube of Holothuria 
tubulosa. By M. EH. Jourpan. 
Throughout its length the intestinal tube consists essentially of 
three distinct fundamental layers—an external or peritoneal cellular 
covering, a fibro-muscular coat, and an inner epithelial layer. 
Outer or Peritoneal Epithelial Layer.—The cells forming this are 
of two kinds. There are simple endothelial cells arranged in a 
single layer ; in their frequently cylindrical form and the presence 
of vibratile cilia they differ widely from the endothelial elements of 
the Vertebrata. Their aspect also varies with the region examined 
and state of contraction or extension of the intestine. The other 
elements, which are much scarcer, are of the type described by 
Semper as mucous cells. 
Muscular Layer.—This is represented by circular and by longi- 
tudinal fibres. The former constitute a continuous and regular muscu- 
lar layer ; the latter are much more numerous in the anterior region 
of the intestine. In the cesophageal region they are internal to the 
circular fibres; at the commencement of the middle intestine and 
throughout the rest of the tube they are placed immediately above 
the peritoneal layer of cells; that is to say, they are external to the 
circular fibres. 
Conjunctive Layer.—In this there is an external zone, in which 
the fibres are intercrossed in all directions and form a close lamina, 
and an internal zone, in which they are much looser. In this part 
of the fibrous coat there are many vacuities; and in it the vessels 
circulate ; it displays numerous nuclei, and some yellow granular 
bodies, like those of the-liquid of the general cavity. 
Inner Epithelial Layer.—This layer presents remarkable diffe- 
rences in the different regions. It is composed of epithelial cells 
and of glandular elements belonging to two distinct types. 
The epithelial cells in the anterior and middle regions are exces- 
sively long, like slender fibrils, and terminate at their free extremi- 
ties in a thick plate. At the beginning of the terminal intestine 
they become true cylindrical cells. 
Of the glandular cells, some have finely granular contents, the 
others a protoplasm like that of the mucous cells so common in the 
