The adult organisation of Paragordius varius. 459 
most important stages of the ontogeny are unknown; discussions of 
general form and mode of life are here not decisive. 
The hypodermis with its thick cuticula resembles that of the 
Nematoda; such a cuticula has been independently acquired, however, 
by such diverse groups as the Nematodes, Trematodes, Acantho- 
cephala, Chaetognatha, and Arthropoda, it is a structure 
quite generally produced by endoparasitic and terrestrial modes of 
life, and hence is of little importance in considering relationships. 
Consideration of the intestinal system is of almost equally small value. 
The absence of a blood vascular system is a character shared by 
all Nematoda, while all free-swimming Annelida have such an 
organ system. But this also is a character of variable value: one 
need but recall the great modifications of the vascular system within 
such a narrowly circumscribed group as the Vertebrata, or as in the 
Annelida, Nemertini and Mollusca. Change of mode of life, relative mode 
of development of other organ systems such as the body cavities and 
the nephridial system, all influence the vascular system, so that one 
is hardly justified in placing reliance upon it as a guide. 
The body muscle tube is composed of a layer of longitudinal 
fibres alone. The Nematoda have also only a longitudinal muscu- 
lature. But some Annelida also have only this layer, thus in 
Polygordius there is no circular musculature (VILLoT). Certainly with 
a thick and resistent cuticula such as the Gordiacea have, a circular 
muscle layer could have no functional value, and hence would not be 
present. VEJDOVSKY has pointed out that the Gordiacean muscle cells 
are formed upon the same plan as those of Annelida, with a non- 
contractile core and a rind of contractile fibrils, and they do not 
show the projecting cell bodies so characteristic of Nematodan fibres. 
I can add another point in which these fibres differ from those of 
Nematoda: the innervation, in ‘all probability, is from their outer, 
hypodermal surface, and not from their inner. Thus the muscle 
structure is of an essentially different type from that of Nematoda, 
and similar to that of Annelida. 
The nervous system of the Gordiacea consists of a ventrally 
placed nerve cord, with an anterior enlargement, the cephalic ganglion, 
and a posterior one (more marked in the female), the cloacal ganglion. 
In the cephalic ganglion there is a ventral fibrous commissure beneath 
the oesophagus, but no nerve cells lie above this commissure, therefore 
there is no cerebral ganglion; in Gordius there is a supra-oesophageal 
fibrous commissure, in Paragordius this is represented by a pair of 
