OF THE llOTATOKIA. 657 



the VorticeUa -hiids from the Aciiietal condition of the Vortieelhe ; but the 

 encysting of the entire body of the latter animal, and especially its resolution 

 into a multitude of gemmules, finds no parallel amongst the liotifera ; hence 

 we cannot regard the two classes of animals as having any close affinity to 

 one another. 



Professor Owen removes the Rotatoria from the Cuvierian group of Radiata 

 and places them amongst the Articulata, in close alliance with the Crustacea. 

 This idea is a plausible one, and has several supporters. But here w^e are 

 met by the fact that all the Crustacea, not excluding the Cirripeds and the 

 Entomostraca, pass through a larval condition, resembling which, notwith- 

 standing the assertion of Leydig, nothing has hitherto been observed amongst 

 the Rotatoria ; whilst the latter cannot be regarded as having any resemblance 

 to the larval conditions of these higher Crustaceans in any stage of their 

 histoiy. Professor Huxley's suggestion, that they are the permanent repre- 

 sentatives of the lam^al forms of his group of Annuloida (including the Echi- 

 noidea, Annelida, Trematoda, and Nematoidea), appears to have many facts 

 in its favoiu", since it connects them with the articulate division of animals 

 without raising them to the level of true Crustaceans. Burmeister and Leydig 

 hold similar ^dews to those of Owen respecting the close relation existing 

 between the Rotatoria and the Crustacea. Leydig dwells especially upon 

 their external figure, the frequently hardened lorica, the existence in their 

 bodies of striped muscular fibre, their nervous system, the anatomical and 

 physiological phenomena of their sexual life, and, lastly, the supposed fact 

 that the young, at its liberation from the o\*um, has not the form of the 

 adult animal, and consequently must undergo a metamorphosis. These argu- 

 ments, when examined closely, afford feeble support to Leydig's opinion. 

 External form is an unsafe criterion of zoological position. Were it trust- 

 worthy, it would bring the Rotatoria nearer to the cilio-brachiate polypes 

 than to the Crustacea. The hardened lorica is nothing more than a modified 

 exo-skeleton, which is as fully developed in the Echinoderms as in the 

 Cmstaceans ; whilst in the majority of the Lerneadse (the section of Crus- 

 taceans to which Rotatoria bear the closest affinity) this hardened integument 

 is wanting. The existence of striped muscular fibre proves nothing, since 

 Mr. Busk long ago discovered this structure in some of the Acalephae, The 

 nervous system of the Rotatoria is as yet so imperfectly understood that little 

 reliance can at present be placed upon our knowledge of it ; besides Avhich, as 

 Professor Huxley has pointed out, a similar condition to that of the supposed 

 nervous system of Rotatoria exists in Turbellaria ; and, lastly, the pheno- 

 mena of sexual life amongst the Rotatoria are as little understood as is their 

 nervous system. The few instances in which male animals have been found, 

 present some resemblance to the phenomena seen amongst the Lemeadie ; 

 but the subject is equally involved in obscurity in each of the two classes of 

 creatures, whilst Leydig's assertion, that the young Rotifera undergo meta- 

 morphosis, appears entirely erroneous. The only facts positively determined 

 indicate that nothing of the kind takes places amongst them, whilst all the 

 Crustaceans, including the Lerneadse, undergo repeated moults before reaching 

 raatuiity. 



We forbear enlarging on this question of the zoological position of the 

 Rotatoria, as it has abeady been discussed in much detail in the first part of 

 this work (p. 468 et seq.). 



The most philosophical mode of subdi\dding the Rotatoria into families 

 is almost as undetermined as their zoological affinities. Ehrenberg, who 

 led the way in this work of classification, based his primary groups 

 upon the number of diAisions and form of the ciliated trochal wreath, sub- 



