ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES, 229 
3. Only a variable proportion of the vascular papillee are perforated. Many, if not 
most, of them are closed and vestigial. 
4, The “lymphatic” spaces are neither true lymphatic nor true blood vascular 
spaces, but partake of the nature of both. We have in the Myxinoids the final stage 
in the separation of the blood vascular from the lymphatic system. In other words, 
the two systems are in the act of segregating out. 
I am indebted for the expenses of this research to a grant from the Government 
Grant Committee. 
It gives me pleasure to acknowledge the kindness of Professor A. Mrrx, M.Sc., in 
placing the resources of his admirable laboratory at Cullercoats at my disposal, and to 
the assistant naturalist, Mr B. Srorrow, for much valuable assistance in carrying out 
the injection experiments. | 
October 1911. 
Postscript, January 1912.—By the courtesy of Dr B. MozrsKxo of Warsaw, I have 
received advance proof sheets of a paper, which by this time will have been published, 
on the morphology of the vascular system of the Lamprey. In this paper Dr 
MozesKo states that the contents of the gill sacs cannot be distinguished from venous 
blood, and he believes the sinus system to be formed during metamorphosis by the 
local enlargement of vascular networks. The sinuses are not present in the young 
Ammoccetes, and only appear shortly before metamorphosis. He concludes that the 
venous system of Petromyzon is not a venous system sensu stricto, but is a 
“systema venoso-lymphaticum,” in which the venous and lymphatic channels are fused 
into a common system, and in which the lymphatic vessels have only partially 
seoreoated out. ‘I'hese conclusions are very similar to those I had already arrived at 
from a study of Myzine. 
EXPLANATION OF THE PLATE. 
Fig. 1. Reconstruction, from serial sections, of the gills, branchial cesophagus, and afferent and efferent 
branchial arteries (coloured red) of a 25 cm. Hag, seen from the left side. x11. The muscles of the gut 
are not included. Afferent and efferent gill ducts are represented cut off at their origin. In the case of the 
common carotid, the branches of the artery are distinguished from the vascular papille by a cut extremity. 
Some of the papilla on the afferent branchial arteries are compound, but the details cannot be shown in a 
diagram of this magnification. For the same reason two very small papille on the first afferent branchial, 
one on the second, and two on the fourth, are omitted. 
Fig. 2. Transverse section of an uninjected afferent branchial artery bearing a vascular papilla with two 
openings into the pleural sac. x50. The division between the artery and the papilla is indicated by the 
broken line. The extent of the epithelial lining of the tubules leading to the exterior is shown by dots. 
Blood vascular cavities coloured red. The drawing is diagrammatic to the extent that both openings did 
not appear in the same section, 
