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EXPLANATION OF PLATES 
All figures unless otherwise indicated are original and were drawn 
with a camera lucida. In closely related species all drawings of the same 
structures are drawn to the same scale, thus permitting direct comparison 
ot hgures. 
SYMBOLS USED 
c, cuticular sheath surrounding proboscis hooks 
cg, cement gland 
g, ganglion of central nervous-system 
gn, giant nucleus 
1, lemniscus 
n, neck 
p, polar prolongation of middle membrane of embryo 
receptacle of the proboscis 
testis 
+3 
July, 1919. 
