SYNOPSES OF NORTH-AMERICAN INVER- 
TEBRATES. 
II. GorpIAcEA (Hair Worms). 
THOMAS H. MONTGOMERY, JR. 
Tue hair worms have been classed by most writers as allies 
of the nematodes, based mainly on the similarity in external 
appearance and in the structure of the body muscular wall. 
The following comparison of more important structural charac- 
ters, however, shows that these two groups are only very dis- 
tantly related, if they are at all genetically connected: 
Gordiacea: Body cavity lined by a peritoneum and trans- 
versed by dorso-ventral mesenteries; two testes in the male ; 
genital aperture in the female united with the anal aperture 
(forming a cloaca); the brain has a narrow dorsal and a large 
ventral commissure, from which passes caudad an unpaired 
ventral nerve (with a ganglionic thickening at its posterior 
end), no dorsal median nerve being present. 
Nematodes : Body cavity not lined by a peritoneum, and not 
transversed by mesenteries ; one testis in the male; the genital 
aperture in the female is never united with, but always anterior 
to, the anal aperture; the brain is a simple ring around the 
cesophagus, and from it pass caudad a dorsal and a ventral 
median nerve. 
Vejdovsky regards the Gordiacea as degenerate annelids, 
basing his view on the metameric arrangement of the ovaries, 
the structure of the body cavity, and the presence of the single 
ventral nerve. But until the embryology of the hair worms is 
better known, their affinities must remain problematical. 
The curious marine worm, Nectonema, whose structure has 
been described by H. B. Ward (Bull. Mus. Comp. Zool., XIII, 
3, 1892), has been regarded by this writer as allied to the 
Gordiacea. But while this affinity seems quite probable, it 
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