140 ON THE STRUCT QRE AND 



upon which it is founded rests upon an erroneous basis. Pvlytrocha 

 and Zyyotrudiu do not exist, nor is it at all admissible, that in many 

 species the gelatinous envelope should be termed a lorica, whilst in others 

 the hardened cuticle should be understood under the same term. Similar 

 criticisms upon Ehrenberg's system have before been made from other 

 quarters, although no one, except Dujardin, has proposed a new arrange- 

 ment. The latter naturalist has endeavoured to arrange the Kotifers by 

 taking the mode in which the movements are effected as the basis of his 

 system ; in accordance with which he has erected the following orders :— 



Ordre I. — Systolides fixe's par un pedicule, 



1. Famille. Flosculariens. 



2. Famille. Melicertiens, 



Ordre II. — Systolides nageurs. 



3. Famille. Brachimiiens. 



4. Famille. Fiircidariens. 



5. Famille. Albertiens. 



Ordre III. — Systolides alternativement rampants et nageants. 



6. Famille. Rotiferes. 



Ordre IV. — Systolides marcheurs. 



7. Famille. Tardigrades. 



With the exception of the Tardigrada, I decidedly prefer Dujardin's 

 system to that of Ehrenberg, founded as it is upon a correct principle of 

 arrangement, and recommended by its simplicity. 



Probably, however, the Rotifera may be arranged according to their 

 forais ; whether they are cylindrico-conical, or sacciform, or compressed, 

 together with which, as further characters, the condition, presence, or 

 absence of the foot, may be employed. Proceeding upon this idea, I 

 would venture to propose something like the following arrangement. 



CiLIOCRUSTACEA. 



Animals with a jointed body and a ciliary apparatus at the cephalic 

 extremity. The nervous system consisting of a cerebral ganglion, and 

 filaments radiating from it. Digestive and respiratory systems much 

 developed. No heart or blood-vessels. Sexes separate. The female pro- 

 duces " Summer " and *' Winter-ova." Many undergoing metamorphosis. 



A. FiGUKE BETWEEN CLAVATE AND CYLINDRICAL. 



I. With elongated, transversely-ringed, attached foot. 



1. Floscularia proboscidea, Ehrenberg ; ornata, Ehr. ; a/'pcn- 



dicidata, n. s. 



2. Stephanoceros Eichhornii, Ehr. ; glacialis, Perty. 



3. (EciSTBS crystaUiims, Ehr. 



4. CoNOCHiLus vol vox, Ehr. 



5. Lacinularia socialis, Ehr. 



6. Limnias ceratophylli, Schrank. 



7. Tubicolaria najas, Ehr. 



8. Melicerta ringens, Schrank. 



The genera Ftygura and Olenophora, Ehr., which, according to their 

 forms, would also belong to this division, do not appear to me to be fully- 

 grown animals at all, bi:t undeveloped forms ; and it is not improbable, 

 as Ehrenberg himself was at one time disposed to believe, that Ftygura is 

 the young of Melicerta ringens. 



