

OF THE ROTATORIA. 479 



Division II. Zygotrocha. 



FAMILIES. GENERA. 



( f with a proboscis and foot-processes CaUidina. 



, , without proboscis : no f , j- i j -rr n • 



eyes absent j i,orn-like processes ^^^^^^ ^^^^^ P^f ^^^.^ . Hydrias. 



[ on the foot . 1 ^^- ^°* P^^^led Typhhna. 



Pliilodinsea i ( i ^o^* ""^^^ horn- f terminal toes two . . . Rotifer. 



two frontal ' ^^® processes \ do. three Actinurus, 



eyes present -l 1 foot without such processes ; terminal 



I L toestwo Monolabis. 



1^ two cervical Pliilodina. 



/eyes absent foot furcate Noteus, 



I J Brachionaea j. J one (cervical) {^ot absent Anuraea. 



^1 I eyes present -^ ^ ^ [ foot furcate Brachionus. 



^ \ [ [ two (frontal), foot sty liform Pterodina. 



Many serious objections attach even to the fundamental principles which 

 Ehrenberg has adopted in his systematic distribution of Eotifera. Leydig 

 has well argued against the existence of an actually compound trochal disk 

 (p. 398) ; and to designate the peculiar ciliated organs of Floscularia and 

 Stephanoceros simple notched wreaths is certainly a misnomer, and conveys 

 an erroneous impression. 



The employment of the " loricated " and " iUoricated " condition, as un- 

 derstood by Ehrenberg, in the construction of families, is even more faulty; 

 for, as before observed (p. 394-5), he uses the term " lorica " so loosely, that 

 it designates no one special structure. The existence and position of eye- 

 specks, as characteristic of genera, are very uncertain and insufficient. These 

 eoloui-ed specks, especially when numerous, are not constant either in number 

 or position ; they disappear with age in numerous instances, in some even 

 before the adult condition is attained ; they may be deficient from various 

 external circumstances of development ; and, in general, they have not that 

 importance in the organization and hfe of the Rotatoria which can warrant 

 their employment as generic distinctions. The formation of the jaws and 

 the number of the apparent teeth might afford valuable characteristics ; but 

 they are facts difficult of determination on account of the minuteness of their 

 pai-ts. From the above considerations it is evident that the descriptions of the 

 Berhn Professor are open to much question, and the generic characters based 

 on them uncertain. 



That this artificial system of Ehrenberg is erroneous, is also evidenced by 

 the separation of undoubtedly allied forms which it often entails. This evil 

 involves another, that of the unnecessary multiplication of genera and of di- 

 stinctive names. Thus Dujardin rightly insists on the erroneous distribution 

 of a naturally single genus, from the really unimportant variation in the 

 number of coloured specks, into the several genera Lepadella, Metoj>idia, 

 Stephanops, and Squamella ; and also indicates the division of the families 

 Philodincea and Hydatincm as carried too far. On the other hand, the ex- 

 tensive genus Notommata comprehends many veiy dissimilar animals, including, 

 for instance, not only such as possess the typical alimentary canal of the 

 Rotifera, but also those recently discovered forms that diverge from that type 

 in wanting a separate anal outlet. Such a genus requires revision. The 

 same may be said of the genus Diglena. In the opinion of many naturalists, 

 the Berlin Professor falls into an additional error in admitting the family 

 Ichthydina among the Rotatoria. In fine, the result of modern research is to 

 call equally in question several of the subdivisions and genera which he has 

 instituted. 



Although the defects and errors of Ehrenberg' s system be generally ad- 



