736 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
is followed by connective tissue ; the latter is connected with the large 
blood-vascular trunk which passes into the head. 
The histological structure of the renal canaliculus is altogether 
different from that of the terminal saccule. The epithelial cells are 
large and polygonal, and so flat as to be worthy of being called pavement 
cells. The side turned towards the lumen has a thick striated cuticle. 
The protoplasm is granular in the part of the cell near the lumen, but 
in the rest has a peculiar structure ; it is arranged in plates which are 
disposed perpendicularly to the surface of the cells. In places, the 
protoplasmic plates of one cell are continuous with the plates of a 
neighbouring cell ; these plates are of irregular thicknesses, and a wavy 
course may be sometimes observed. Dr. Grobben states that his earlier 
view that the plates are arranged parallel to the contour of the nucleus 
was incorrect. 
In cross-section the protoplasmic plates appear as rods, and have, 
therefore, the same appearance as the so-called rods in which the pro- 
toplasm of the kidney-cells so often appears to be arranged. The plates 
may be supposed to have arisen from protoplasmic rods set in order one 
behind another, and fused with one another. A similar disposition has 
been observed by the author in the renal cells of Sepia, and by Eabl in 
the oral epithelium of the larva of the Salamander. 
The ureter has the same structure as the integument, of which it is 
an invagination. The wall consists of small cells with a cuticular 
lining on the side nearest the lumen. 
Arterial System of Isopods.* — M. A. Schneider points out that in 
Isopods there is a vascular collar anterior to the nerve-ring, which 
supplies the arteries of the oral appendages. In Annelids, however, as 
well as in Myriopods and Arachnids, the analogue of this vessel is 
situated behind the brain. He has made some injections of Porcellio and 
Lygia, which show that the condition which obtains in Isopods is not 
really anomalous. In them, there are, behind the nerve collar, two 
arteries which arise from the aorta in the immediate neighbourhood of 
the point of origin of the ophthalmic artery. The course which they 
follow shows that they form a ring in every way comparable to that of 
Arachnids. The author has also been able to show that in Porcellio and 
Lygia the ophthalmic and antennary arteries form a vertical vascular 
ring which recalls that of Amphipods. He has, therefore, been able to 
show that the previously supposed unique arrangement of Isopods is not 
a true morphological peculiarity, and that they do not differ from 
Amphipods, as has been believed. 
Development of Germinal Layers of Isopoda.|— M. L. Roule has 
studied the early development of Porcellio scaber. He finds that the 
blastoderm proliferates in several regions, and on the internal surface ; 
but, notwithstanding the organs to which it gives rise, it does not 
lose the appearance of a simple epithelial layer set around the nutrient 
yolk. It retains this appearance even after the mesoderm and endoderm 
have been formed at its expense, and have become separated from it ; 
and it then represents the ectoderm. 
* Comptes Itendus, cxiii. (1891) p. 316. f Op. cit., cxii.(1891) pp. 1460-2. 
