*jourS juSrST Filamentous Algie for the Mieroseo^e. 361 
The capillaries, shortly after their origin, bend outwards away 
from the large vessels, and, piercing the retina vertically to its 
stratification in a direction more or less radial from the centre of 
the globe and branching dichotomonsly in the granular and inner 
granule-layers, they form loops, the outermost of which reach the 
intergranule-layer. As they enter the retina the membrana limitans 
interna is prolonged upon the capillaries in the form of a sheath, 
which is wide and funnel-like at first, but soon embraces the vessels 
so closely as to become indistinguishable from their proper wall ; so 
that, notwithstanding the existence of a sheath, there is no peri- 
vascular space about the retinal capillaries, such as His has described 
in the brain or spinal cord, and has stated to occur in the retina 
and elsewhere. 
In all other mammals, except the hedgehog, as far as my present 
knowledge extends, the arteries, veins, and capillaries lie in the 
retina. In fish, amphibia, reptiles, and birds, however, as H. Miiller 
and others (myself as regards amphibia and reptiles) have shown, 
the retina is absolutely non-vascular, the absence of proper retinal 
blood-vessels being compensated for in fish, amphibia, and some 
reptiles by the vascular net which in these animals channels the 
hyaloidea, and by the highly vascular pecten present in other 
reptiles and in birds. Thus it is possible to divide vertebrates into 
two classes, according as their retina is vascular or non-vascular ; 
and these classes would be connected by the hedgehog, the larger 
branches of whose vasa centralia lying upon the membrana limitans 
in intimate relation with the hyaloidea, represent the equivalent 
vessels of the hyaloid system, which forms so exquisite a micro- 
scopic object in the frog ; whilst the capillary vessels channelling 
the retinal tissues occupy the same position which they do in most 
mammaha. 
[The drawings in illustration of this paper are preserved for 
reference in the Archives of the Eoyal Society.] — Proceedings of 
the Boyal Society^ May, 1867. 
YIII. — A new Process of Prejoaring Sjoecimens of Filamentous 
Algse for the Microscope. By A. M. Edwards. 
The working microscopist well knows how little really valuable 
information, of a practical character, is to be found in books pro- 
fessing to treat of the subject of preparing and mounting specimens 
of the lower families of Algae, so as to exhibit in a satisfactory 
manner the characters which distinguish them in a generic or 
specific manner. This remark also applies, although with not so 
