CHAPTER XI. 
Order IV. SCIRTOPODA. 
Swimming with their ciliary wreath, and skipping with Arthropodous limbs ; foot 
absent. 
The fourth order, Scirtopoda, although it contains but two Rotifera, each in a genus 
by itself, is one of no little importance, as it is that in which the Rorirera and Crus- 
TACEA most nearly touch. The true position of the Rotrrera in the animal kingdom 
has long been a matter of keen dispute, and the chief authorities have taken opposite 
sides: Professor Owen, Dr. Leydig, and others, rank them among CrustacEa!; while 
M. Milne-Edwards, Dr. Cohn, Professor Huxley, with the majority, would consider them 
as VERMES. Nor is this surprising; for the Rorirmra possess many characters that are 
common, in various degrees, to ARTHROPODA and VERMES alike; and, so far as their nutri- 
tive, reproductive, or nervous systems are concerned, might with little difficulty be placed 
in either sub-kingdom. But there were three respects, before the discovery of Pedalion and 
Hexarthra, in which the Rorrrera appeared to differ from ARTHROPODA, and to resemble 
VERMES. These are, first, that they do not possess pairs of jointed appendages, articu- 
lated to the body, with muscles prolonged into their interior; and on this point great 
stress was laid. Secondly, that they swim by means of ciliary wreaths; and thirdly, 
that they possess a vascular system, with ciliated tags, whose chief function is probably 
a respiratory one. 
But the discoveries of Pedalion and Hexarthra have shewn that Rotifera exist whose 
internal structure is perfectly normal, and which yet possess three pairs of unquestion- 
ably Arthropodous limbs ; and these discoveries have in consequence disposed of the chief 
objection to the ranking of the RormrrRA among ARTHROPODA. It may, on the other hand, 
be fairly urged that the balance of argument even now inclines towards those who are 
in favour of the opinion that the Rorrrra, as a class, are nearer to VERMES: yet no 
one, I think, who has studied both Pedalion and the Nauplius larva of one of our 
fresh-water ENromostRaca, would feel satisfied with their being placed in two distinct 
sub-kingdoms. 
In conclusion, I see no reason why the Rortrera should be assigned solely to VERMES 
or ARTHROPODA; and I would propose to consider them as a class that links these two 
sub-kingdoms toyether.? 
Family XX. PEDALIONIDA. 
Arthropodous limbs siz ; head trwncate; corona of two concave lobes ; ciliary wreath 
as in Philodinade ; trophi malleo-ramate. 
The family contains two genera, Pedalion and Hevarthra, each containing only 
a single species. The two are much alike* in the possession of six Arthropodous limbs 
' {I consider the Rotrrera a class of the sub-kingdom ARTHROPODA, co-equal in rank with 
Insecta and Crustacra.—P.H.G.] 
* Of course I am here treating the matter simply as one of formal classification; and from this 
point of view it is enough to say that if we knew none but the humbler forms of the Rorirera, we should 
call them VERMES; whereas if Pedalion and Hexarthra were our only examples, we should call them 
the lowest forms of ARTHROPODA. 
* Mr. Julien Deby, in the J. Roy. Micr. Soc. 1879, p- 384, has suggested that the two Rotifera are 
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