
792 THE AMERICAN NATURALIST. [Vor. XXXVI. 
the veins, so that it is certain that the vascular system was 
fully injected. Serial sections of many portions of the squid, 
and gross mounts of portions of the skin, mesentery, and 
intestinal wall show conclusively that there is a perfect capil- 
lary network which connects the arteries and veins in all parts 
of the body. Like other capillaries, these (Fig. 4) branch and 
anastomose frequently without altering their diameter, and their 
walls are formed by an endothelium composed of flat oval cells 
with sinuous margins. The silver impregnations of the capilla- 
ries, though rarely successful, leave no doubt as to the nature of 
the wall. 







Fic. 4. — Artery, i ins, and 
Hets 3 £. ah norting 
T o E rE 
b f the gill. æ, artery; v, veins. 

Some arterioles and capillaries are connected with lacuna- 
like cavities which may be called the end sinuses of the veins. 
Fig. 5 is a camera sketch of such a sinus situated in the 
visceral body wall. Similar sinuses have been found in the 
testis, glands, and muscles, and it is very probable that they 
are more widely distributed. Each sinus is a small irregular 
cavity, into which an arteriole passes and then breaks up into 
branches; the latter pass out of the sinus and communicate 
with the surrounding capillary plexus, some of whose branches 
_ open into the sinus, so that the blood must pass through the 
~ perforating arteriole and then through the capillaries into the 
