MR. R. OWEN’S REMARKS ON THE ENTOZOA. 393 
Having been thus led, in considering the place which Trichina ought to occupy in 
the natural system, to review the arrangements of the Entozoa generally, to trace their 
affinities to the other classes of Radiata, and thus to take into consideration the grounds 
for retaining or otherwise that division of the Animal Kingdom, I now proceed to consi- 
der the Entozoa which are separated from the Sterelmintha, and examine them in relation 
to the classes of the Radiata which remain after the dismemberment of the Acrita. 
The Vers Cavitaires of Cuvier, which include the Nematoidea of Rudolphi and the 
Vers Rigidules of Lamarck, together with the genus Nemertes, and the genus Linguatula 
(Pentastoma, Rud.) previously described, I propose to separate into two classes ; the 
one including, with the Nematoidea, the genera Linguatula and Sipunculus, under the 
term Celelmintha' ; the other formed by the Vers Rigidules under the term Epizoa, which 
the researches of Dr. Nordmann have recently shown to exhibit a much higher type in 
their free moving condition than many of them afterwards exhibit when they have 
become fixed to the animals which they infest. 
Both these classes have a condition of the nervous system in common with the Echi- 
nodermata and Rotifera of Professor Ehrenberg, which may be termed the filamentous, 
since, in all these animals, simple ungangliated nervous filaments can be traced, extend- 
ing from a point near the commencement of the alimentary canal, in number and direc- 
tion corresponding with the form of the body. This condition of the nervous system is 
accompanied by a distinct development of the muscular system, and especially of a 
muscular tunic of the alimentary canal, which now floats in an abdominal cavity, and, 
with the exception of one family of Echinodermata, has a distinct anus. There is no longer 
in this division any instance of fissiparous or gemmiparous reproduction. In the Echino- 
dermata, which are allied to the Polypi vaginati by the fixed pedicellate Encrinites, the 
nutritious fluid circulates in distinct arteries and veins; and in the Holothurie, express 
respiratory organs are superadded. From the Echinodermata which present this length- 
ened worm-like form, together with the softening down of the external crust, the Sipun- 
cult make an easy and natural transition to the Celelmintha, to which class, from the 
absence of respiratory organs and tubular feet, from the obscure traces of a vascular 
system, and the disposition of the nervous filaments, they appear to me to have closer 
affinities than the Echinodermata. 
The Celelmintha, thus constituted, present the same varieties in the condition of the 
generative system as the Sterelmintha. We find the simple female apparatus without 
male organs, or the cryptandrous type, in the Sipunculi; the superadded male glands, 
but without reciprocal fecundation, in the Linguatula; and the separate sexes in the 
Nematoidea. 
If we distribute the internal parasites of the human body according to the preceding 
attempt at a natural arrangement of the Entozoa, they will be found to belong to at 
least three distinct classes of animals. 
} cowNos, cavus, éAyuvs, lumbricus. 
