458 THOS. H. MONTGOMERY jr,, 
The older investigators of the Gordiacea classed them with 
the Nematoda. The points of structure on which this grouping 
was made, were: the elongated form, the thick external cuticula, the 
presence of a single layer of longitudinal muscles, the absence of 
distinct segmentation, the tubular character of the reproductive organs, 
and the lack of a blood vessel system. Even to-day in most of the 
zoological text-books the Gordiacea are classed with the Nematoda 
together in the group of the Nemathelminthia; by others as no 
more than a family of the Nematoda. von Lınstow (1897) divides 
the Nemathelminthes into three groups: the Secernentes, the 
Resorbentes, and the Pleuromyarii, and includes in the latter 
such heterogeneous forms as Trichocephalus, Trichosoma, Gordius, 
Nectonema, Mermis and Echinorhynchus. All the various classifications 
of the Gordiacea under the Nematodes need not be repeated here, 
since VıLLoT (1874), VEIDOVSKY (1885) and CAMERANO (1897) have 
mentioned them in their historical sequence. 
A smaller number of authors have questioned the relationship to 
the Nematodes. Thus von SIEBOLD (1843) classed the Gordiacea 
as an independent order equivalent to that of the Nematodes. GRE- 
NACHER (1868) with his usual critical acumen also emphasized the 
great degree of structural difference between these groups. Then 
VitLot (1874) concluded that it is necessary to establish for the 
Gordiacea a special order, to be placed at the head of the class 
Helminthes; but he later (1881) referred them to the Nematodes. 
VEJDOVSKY (1886) concludes that they are “degenerirte Annulaten.. . 
und vorläufig als eine selbständige Ordnung der Nematomorpha 
zu unterscheiden”; and in 1894 he states: “Ueber die verwandtschaft- 
lichen Beziehungen der Gordiiden zu andern Wurmgruppen darf man 
sich erst dann bestimmter aussprechen, wenn die eigentliche Larve (der 
Embryo der Autoren) genauer in ihren Organisationsverhältnissen be- 
kannt ist”. CAMERANO (1897) makes two orders of the Nemathel- 
minthes, the Nematodi and the Gordiacei, the latter com- 
prising the two families Nectonemi and Gordiidi, the phylum of 
the Nemathelminthes and that of the Annelida connecting only at their 
roots (in the group of the Provermalia). 
We have accordingly to consider whether the Gordiacea show 
affinities to the Nematodes or to the Annelida, or whether they 
should be considered an independent phylum ; for possible relationships 
with any other living groups are too vague to be treated. We have 
to do with interpretations of adult structural resemblances, since the 
