LACINULARIA SOCIALIS 12/ 



the close alliance between MegalotrocJia and Lacinularia, for a reason 

 which will appear in the sequel. 



The globular aggregations of which I have spoken are not ramified 

 animals like the freshwater Polyzoa, to which, at first sight, they have 

 no small resemblance, but may be truly called compound animals, since 

 each of the Lacinularia is a separate individual, which at one time 

 swam about freely by itself,^ which has voluntarily united itself with 

 its fellows, and has taken its share in throwing out the gelatinous 

 substance which connects them into a whole. 



¥,a.c\\ Laciiiularia (PL I. [Plate 14] fig. i) has an elongated conical 

 body, whose outer extremity is considerably the wider, and whose inner 

 smaller end is truncated, and serves as a sucker or means of attachment 

 to the stem on which the whole mass is seated ; the outer third or 

 fourth of the body contains the viscera, nothing but the muscular 

 cords extending into the inner narrow elongated part of the animal. 

 During contraction, the latter portion is thrown into sharp folds, 

 while the visceral portion presents only three or four faint transver.se 

 constrictions. 



When the Rotifer is in a state of expansion and activity, its outer 

 extremity is termina';ed by a large horseshoe-shaped wheel -organ, or 

 ^' trochal disc " (figs. 2, 3), connected with the body by a narrowed 

 neck. When contracted and at rest, the whole of this apparatus is 

 drawn in, and the body takes on a more pyriform appearance (fig. 5). 



The mouth lies in the notch of the trochal disc (fig. 4.d) ; the anus 

 is placed on the opposite side, at the lower part of the visceral portion 

 of the animal {k). 



Anatomy of Lacinularia. — I will now proceed to describe the 

 various organs of the animal more minutely. 



The " trochal disc " is, as I have said, wide and horseshoe-shaped. 

 It is seen in profile at figs, i and 2 ; from above at fig. 3. Its edges 

 are richly beset with large cilia, which present a very beautiful wheel- 

 like movement. 



Ehrenberg says that the ciliary organ is " as in Megalotrocha" and 

 in this he describes the disc as having a simple ciliated edge. I have 

 not examined MegalotrocJia, but I can say most decidedly that such 

 is not the structure of Lacinularia? 



^ Or rather had the power of swimming about freely ; for it does not appear that the 

 young Lacinularia ever do leave the gelatinous envelope of the parent mass, unless aggregated 

 together. 



^ Leydig (Zur Anatomie und Entwickelungs-geschichte der Lacinularia socialis— 

 Siebold and Kolliker's Zeitschrift for February, 1852) says that "an elevated ridge runs 

 along the lower surface of the wheel-organ, not far from, and parallel to, its margin, 

 whence there is a double edge and a groove, in which alone ciliary motion is observed." 



