142 LACINULARIA SOCIALIS 



while the upper circlet of large cilia does not encircle the axis, but lies 

 in the lower and anterior region of the body. 



If the region behind that ciliary circlet which is traversed by the 

 axis be called the post-trochal region, and that in front of it the pre- 

 trochal region, we find that the circlet of large cilia is developed in the 

 inferior pre-trochal region. 



Now compare this Rotifer with the larva of an Annelid. It will 

 be immediately .seen that the two are of essentially the same type, 

 only that, while the Annelid larva is equally and symmetrically 

 developed in all its regions, and has frequently no accessory ciliated 

 bands, the Rotifer has its superior post-trochal and inferior pre-trochal 

 regions developed in excess ; so that the anus is thrown to the ventral, 

 while the mouth is thrust towards the dorsal surface,^ an accessory 

 ciliated circlet being at the same time developed in the latter region. 



Mcliccrta ringens (compare figs. 26-28) resembles Lacinnlaria in 

 the arrangement of its ciliated bands, only they are far more distorted 

 from their normal circular form. Tubicolaria closely resembles 

 Melicerta, 3.nd there can be little doubt that Megalotrocha and Limnias 

 are to be added to this division. 



In Brachionus, Philodina, Rotifer, Notonnnata, the same fundamental 

 type obtains, but the deviation from symmetry takes place in a 

 different ws.y. 



In all these it is the ventral post-trochal region which is over- 

 developed, and therefore the anus is thrown to the dorsal or ganglionic 

 side. 



In Notoinmata the trocha appears to be simple and unaltered in 

 most species, and there is no accessory circlet. 



In N. aitrita, however, as it appears from Mr. Gosse's description, 

 and in Brachionns poly acanthus (figs. 30-33), several processes, three in 

 the latter case, are developed from the superior pre-trochal region. 

 They are richly ciliated, and appear to represent the accessory circlet 

 of Lacinularia. 



Another distinct type is presented by Pliilodiiia (figs. 34-37). In 

 this the great trocha is bent upon itself, and the anterior division of it, 

 at first sight, simulates an accessory circlet developed in the superior 

 pre-trochal region. It is not so, however, as the continuity of the band 

 of cilia can be readily traced throughout. 



To this division of the Rotifera, viz., those which have the anus on 

 the same side of the body as the ganglion, appear to belong the genera 



1 This over-developmenl is not a mere matter of hypothesis. The yoimg Lacinularia 

 has the anus nearly terminal and the "peduncle" only subsequently attains its full 

 proportiims. Compare fig. 17 and fig. iS, PI. I. [Plate 14]. 



