284 Characteristics of Rotifers. 



from the Greek, arvarokr], contraction, but as many other crea- 

 tures exhibit contractibility in as remarkable a way, the name 

 has not usually beenconsiderecl appropriate, and has not come into 

 general use. He divides his Systolides, which include water 

 bears, into orders, as follows: — 1. Those which are fixed 

 by the posterior extremity of their body. 2. Those which 

 have only one mode of locomotion by means of their vibratile 

 cilia, or the swimmers. 3. Those which have two modes of 

 locomotion, and which sometimes crawl like leeches, and at 

 others swim like the preceding, or swimmers and crawlers. 4. 

 Those which are destitute of vibratile cilia, but provided with 

 claws and are veritable walkers — water-bears. It is desirable 

 to exclude the water-bears from the group, and we shall then 

 have fixed rotifers, swimming rotifers, and swimmers and 

 crawlers. These divisions, though not founded upon any deep 

 considerations of structure, indicate obvious and important 

 facts. The fixed rotifers comprehend the Floscularians, which 

 have long tufts of cilia, but no wheel-like organs, and the Meli- 

 certians, which have four lobes something like the petals of 

 a flower, with cilia round their margins, exhibiting the rotatory 

 appearances. The swimmers comprehend several genera, 

 amongst which the Brachions, or pitcher rotifers, are conspicu- 

 ous. Dujardin proposes two divisions of swimmers, one cha- 

 racterised by a general flexibility of the skin or integument, 

 Furcularians, and the other, like Bracldonus, Saljnna, etc., hav- 

 ing rigid carapaces or cuirasses. The swimmers and crawlers 

 comprehend the Philodines, of which the common rotifer is the 

 type. Many things might be said against accepting this 

 scheme as a final arrangement of the group, but no harm can 

 arise from its provisional use, provided that it is borne in mind 

 that in addition to the modes of locomotion mentioned by 

 Ehrenberg, jumping must be added as characteristic of several 

 species, such as Polyarthra, Triarthra, and a few others. It 

 would also be advisable to add to Dujardin' s groups one of 

 associated rotifers to include Conocliilus and Lacinularia, 

 which are inconveniently placed in his Melicertian family. 

 There is an obvious and important difference between the per- 

 manent fixture, with confinement to one spot, of the Floscules, 

 Melicerta, (Edstes, etc., and the free swimming of the asso- 

 ciated groups of Conochihis. In both cases the creatures may 

 anchor themselves by their tail-feet, but in one case there is 

 permanence of abode and in the other a roving life. 



The fixed rotifers differ very considerably from each other, 

 and those which form simple tubes are easily distinguished 

 from the MelicertcB, which are builders, constructing their 

 abode of separate pellets moulded by an organ specially pro- 

 vided for the purpose, and placed in due order as a mason 



