No. 430.] THE COMMON SQUID, LOLIGO PEALII. 793 
sinus! The sinuses are connected with the veins by very small 
vessels. In partially successful injections the colored arteriole 
can be seen surrounded by a space filled with blood corpuscles, 
but in perfect injections both the arteriole and the sinus are 
filled with the injection mass. The arteriole, capillaries, and 
the sinus are all lined by endothelium. It was impossible to 
determine whether the endothelium of the sinus was reflected 
over the surface of the perforating arteriole. It is worthy of 
note that when the blood had not been driven out of the sinus 
the proportion of corpuscles in the blood of the sinus was six 
or eight times as great as in the other vessels, —a fact which 

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Fic. 5. — End sinus of vein, from visceral body wall. 
may be due to the filtering out of the corpuscles as the blood 
was driven through the vessels by the injection fluids. 
The Capillaries of the Gills. —The gills are not easily injected 
because a valve at the origin of the branchial artery prevents 
the free flow of injection fluids in either direction. The valve 
is formed by four tubercles which project in the direction of the 
blood current into the lumen of the artery. A band of muscle 
fibers forms a sphincter whose contraction forces the tubercles 
together so that the lumen of the vessel may be closed. 
1 The connection between these vessels and the veins has been inferred from 
the course of the injection fluids through the sinus. 
