ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 217 
are concerned ; (2) subsequent treatment is difticult. The mass expands and contracts 
according to the amount of water present. It contracts considerably on dehydration, 
and expands again if the sections are stretched on water on the slide. Preparations are 
completely ruined as regards the finer details if they are placed after injection in formalin 
or weak alcohol, owing to the excess of water producing expansion of the gelatine and 
consequent rupture of the tissues. Further, gelatine becomes brittle and difficult to 
handle in parattin. 
Syringes must be avoided. It is difficult to regulate the pressure, and still more 
difficult to inject with the minimum pressure required. Syringe injections generally 
“blow off” the tops of the papille, and what appears to be a demonstration of the 
communication is only an illustration of the crudeness of the method. 
What I regard as a convincing proof of a connection between the artery and the 
surrounding sinus wa the papille may be readily obtained in the following way. The 
injection fluid is a simple solution of Prussian blue in distilled water. This is placed 
in a glass vessel which is raised about five feet above the laboratory bench, and an 
india-rubber tube leads from it to the bench, and has at its end a glass cannula drawn 
out to a capillary tube. The flexible tubing is closed by a screw clamp placed just 
above the cannula. The base of the latter may be passed through a cork, so that when 
it is in position in the vessel from which the injection is to be made, the whole can be 
held and kept steady by the clamp of a retort stand, leaving both hands of the observer 
_ free. Immediately the animal is motionless it is strapped down under sea-water, and 
the ventricle and ventral aorta are exposed. The free extremity of the ventricle is 
snipped off, and the cannula pushed into the root of the aorta and a ligature applied. 
The afferent branchial arteries may now be carefully exposed under a Braus-Druner 
_ dissecting microscope by removing the external walls of the pleural sacs, and the whole 
_ of the subsequent operations kept under continuous microscopic observation, since all 
_ that is needed to start the injection is to slightly turn the screw of the clamp. The 
speed of the injection is thus under complete control, but to demonstrate the openings 
_ of the papillee without rupture, as the latter are clearly the weakest points of the arteries, 
the injection fluid should be allowed to pass very slowly into the ventral aorta. Watch- 
‘ing the papillee under the microscope, and in the living animal they are more or less 
transparent, the injection is seen to pass immediately into the large cavity at the base 
of the papille (figs. 2, 3, 5). Then fine blue threads spring out, connecting this cavity 
with the apex of the papilla. There is a slight pause, and finally delicate spirts of 
blue are discharged from the papilla into the cavity of the surrounding sinus. It seems, 
therefore, that when the pressure in the artery is low, there will be no discharge of 
blood into the sinus, but that when the pressure rises beyond a certain limit, blood is 
transferred from the cavity of the artery to that of the peri-branchial lymph sinus or 
pleural sac. 
The use of an injection medium which is a cold solution, ensures an easy passage into 
the finest vessels, and as it is readily precipitated by the addition of aleohol—in fact it may 
