THE VASCULAR SYSTEM OF THE COMMON 
SQUID, LOLIGO PEALII. 
LEONARD W. WILLIAMS. 
THE knowledge of the histology of the vascular system of the 
decapod mollusks is very incomplete. The nature and extent 
of the capillary system especially have been so little understood 
that two contrary opinions find expression in the text-books of 
zoólogy. It has been maintained by Lang that the arterial and 
venous systems are connected partly by capillaries and partly 
by lacunze, which are portions of the primary body cavity, while 
Parker and Haswell affirm that the blood flows through a com- 
plete system of capillaries. I have been unable to find any 
published work which decides between these views. All agree 
that the vascular system is highly developed and that the capil- 
lary system is extensive, but no one seems to have investigated 
the structure of the vessels or to have determined the exact 
nature of the so-called lacunz or sinuses. Prof. Ulric Dahlgren 
called my attention to this subject, and under his direction I 
worked upon the vascular system of the squid at Woods Hole 
during the summers of 1899 and 1900, and at Princeton Uni- 
versity during the intervening time. The material, Loligo 
£eaíii, was furnished me by the Marine Biological Laboratory 
through the kindness of Professor Dahlgren, and by the United 
States Fish Commission through the kindness of Dr. H. C. 
Bumpus, and further material was obtained from the traps at 
Elberon, N. J. ; 
The extent of the capillary system was determined by inject- 
ing the vessels with a saturated aqueous solution of Berlin blue. 
The injected tissues were studied while fresh and transparent 
or were fixed in acetic corrosive sublimate er 95 per cent 
alcohol and mounted in serial sections. The structure of the 
walls of the vessels was studied after impregnating them with 
silver in order to show the outlines of the endothelial or other 
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