CHAPTER XI. 



Order IV. SCIRTOPODA. 



Swimming with their ciliary ivreath, 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 ROTIFEKA and CRUS- 

 TACEA most nearly touch. The true position of the ROTIFERA 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 VEKMES. Nor is this surprising ; for the ROTIFERA possess many characters that arc 

 common, in various degrees, to AETHBOPODA and VEEMES 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 ROTIFERA appeared to differ from ABTHEOPODA, and to resemble 

 VEEMES. 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 ROTIFERA among AETHEOPODA. 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 ROTIFERA, as a class, are nearer to VEEMES : yet no 

 one, I think, who has studied both Pedalion and the Nauplius larva of one of our 

 fresh-water ENTOMOSTRACA, would feel satisfied with their being placed in two distinct 

 sub-kingdoms. 



In conclusion, I see no reason why the ROTIFERA should be assigned solely to VEEMES 

 or AETHEOPODA ; and I would propose to consider them as a class that links these two 

 sub-kingdoms together. 2 



Family XX. PEDALIONID.E. 



Arthropodous limbs six ; head truncate; corona of tivo concave lobes ; ciliary wreath 

 as in PhilodinadcB ; tropM malleo-ramate. 



The family contains two genera, Pedalion and Hexarthra, each containing only 

 a single species. The two are much alike 3 in the possession of six Arthropodous limbs 



1 [I consider the EOTIFERA a class of the sub-kingdom AETHEOPODA, co-equal in rank with 

 INSECTA and CRUSTACEA. 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 EOTIFERA, we should 

 call them VEEMES ; whereas if Pedalion and Hexarthra were our only examples, we should call them 

 the lowest forms of AETHEOPODA. 



3 Mr. Julien Deby, in 'the J. Roy. Micr. Soc. 1879, p. 38-1, has suggested that the two Eotifera are 



