BLOOD-VASCULAR SYSTEM OF THE LORICATI 33 
its action toward gelatin is favorable, hardening it considerably. 
The coats of the eye are fixed in perfect shape, and such deli- 
cate organs as the kidneys are quickly hardened, so that one 
can cut cross-sections with a knife, which is a great help in 
tracing out the renal-portal system. 
If a histological injection is required, slit the s7us venosus 
and wash out the blood vessels, cephalad, from the dorsal aorta; 
then inject with an aqua or thin gelatin Berlin blue mass, or 
with Hoyer’s yellow chromate mass, freshly prepared. The 
mass is allowed to set and the injected organs are thrown in 
toto into Miiller’s fluid, or better still, cut up into small pieces 
and thrown into any well known fixing fluid that will not extract 
the colors. Injected material thus fixed can be kept some 
months in alcohol, but it is best to imbed as soon as possible. 
If the bile vessels are to be injected, it can be accomplished 
by slitting the ductus choledochus, near its exit into the intestine 
or pyloric ceca. A hypodermic syringe filled with the Berlin 
blue mass is inserted into the duct, toward the gall-bladder, fill- 
ing first the bladder, then the hepatic ducts, and finally, if suc- 
cessful, the gall-capillaries. 
III. HISTORICAL REVIEW. 
To Duverney (13),* in 1699, 62 years after the discovery of 
the blood-vascular system by Harvey, and 38 years after the 
discovery of the capillaries by Malpighi, belongs the honor of 
first explaining the structure of the fish heart; and 2 years later 
(14) he described and figured the circulation in and about the 
gills of the carp; he erred, however, in finding but one branchial 
vessel in a branchial arch. Monroe (48) in 1787, was the first 
to describe correctly the circulation in the gills. He injected 
the ventral aorta and examined the gill-filaments under a micro- 
scope; he also noticed the efferent branchial vessels, uniting to 
form the carotids, cceliaco-mesenteric, dorsal aorta, and the sub- 
clavians, and observed the coronary and other vessels coming 
from the ventral ends of the efferent branchial vessels; as well 
as the jugular, portal, and renal-portal systems. According to 
Miiller (50), Albers (1) in 1806, was the first to notice the cho- 
roid gland of the eye, and observed that the vessels in the cho- 
* All figures in brackets refer to bibliography at the end of the paper. 
