470 GENEKAL HISTOEY OF THE INFUSOKIA. 



differences from them, their alHance with them must be admitted. Making 

 due allowance, therefore, for the vibratile cilia and the peciihar respiratory 

 apparatus of Rotatoiia, Leydig would constitute them a special class of 

 Crustacea, under the name of Ciliated Cnistacea. 



The foregoing arguments of Leydig for the Crustacean nature of Rotatoria 

 have been severally met and replied to by C. Vogt, in a recent paper " On 

 the Systematic Position of the Rotifera " {Zeitschr. 1855, p. 193). The ob- 

 jections advanced are these : — 



That Leydig assigns an undue importance to external resemblances ; and 

 that, as to movements, there is as much similarity between those of PhilocUna 

 and a leech, as between those of any other of the Rotifera and the skipping 

 motions of Entomostraca. The figm^e is no actual evidence of affinity : no 

 perceptible likeness exists between fixed Rotifera, or a sac-hke Notommata 

 and a Crustacean, whilst, on the contrary, an imdoubted similarity prevails 

 between a Stejpluuioceros and a Bryozoon ; and between Notommata tardigrada 

 and many of the Vermes the resemblance is more pronoimced than that be- 

 tween any of the Rotatoria and a water-flea. Besides, there are Vermes of a 

 smooth, oval, discoid, and expanded figm^e, and others with bodies not less 

 clearly di\'ided into regions than the Rotifera. 



An annulate articulation, like that of the pseudopodium of Rotifera, is also 

 a feature seen among Annelida ; and the telescopic joints and movement are 

 witnessed in Eunice. It is the possession of limbs, each consisting of several 

 segments, which is characteristic of Articulata, both in the full-grown and 

 in the larva condition, and not an asymmetrical process actually forming but 

 a single segment. Further, spines and hooks, in some degree moveable like 

 the pincer-processes on the pseudopodium of Rotatoria, occiu' in many Vermes, 

 especially among the parasitic species. Lastly, a pair of jointed locomotive 

 organs is never foimd among Rotatoria at any period of theii- existence. The 

 assertion that the thickening of the integument as a lorica is not seen in any 

 Vermes is correct, if the constitution of the lorica of one piece be a necessary 

 feature, although the thick cartilaginous tube of Gordiacece and the firm in- 

 tegument of many other Annehds may be adduced as analogous conditions. 

 But if a lorica may be composed of several pieces, the whole family of marine 

 Annelida, in which the skin is hardened into a firm shield, may be cited as 

 homologous. To Ley dig's remark that he knows of no Vermes with a lorica, 

 the rejoinder may be made, that no Crustacean is found enveloped in a gela- 

 tinous sheath, like Notommata cenfrura, whilst, on the contrary, such an 

 investment is common among Vermes, and especially exemplified in Si^hono- 

 stomum. 



Striated muscles are not unknown in Annelida ; they have been seen in 

 Salpa ; and in some Radiata the particles of muscles separate as so many 

 disks. Moreover, such muscles occur in other Invertebrata besides Crustacea, 

 and they therefore furnish no real argument for allying Rotifera with the 

 latter. 



The nervous system lends no support to Leydig's views, as he professes it 

 does. A coalesced cerebral gangUon sending off neiwes to depressions in the 

 cuticle armed vdth bristles, finds no analogy among the lower Crustacea, but 

 exhibits, on the other hand, an actual identity of structure ^vith the nervous 

 system of the Turbellaria. The same resemblance is apparent among all the 

 Cestoidea, the Nemertm, Planar ia', and Trematoda. Again, the like degrees 

 of development of eye-specks, from a simple heap of pigment to a definite 

 organ with a refracting medium, is illustrated by all those sections of the 

 class Vermes, as Quatrefages shows in his figm-es of the Nemertce. The mode 

 of termination of the nerves described by Leydig in Rotatoria and Crustacea 



