ACALEPH^C. 229 



double-bell-shaped animals, one fitting into the cavity of the other ; 

 Phijsaliadse, having large oblong air-vessels and numerous tentacles 

 of several forms, long, and pendent from one end of the shell, with a 

 wrinkled crest ; VileUadss, animals stretching over a cartilaginous 

 plate with a flat body, an oblique, vertical, cartilaginous crest above, 

 a tubular mouth below, and surrounded by numerous short tentacles ; 

 Physophora, consisting of a slender and vertical axis, terminating in 

 an air-bladder, carrying laterally swimming-bladders, which lose 

 themselves amongst a bundle of slender white filaments. 



VlLELLADJE. 



The Vilellse assemble together in great shoals ; in tropical seas and 

 even in the Mediterranean they may be seen in fine weather floating 



Fig. 93. Vilella limbosa (Lamarck). 



on the surface of the waves. As described by De Blainville, the body 

 is oval or circular, and gelatinous, sustained in the interior of the 

 dorsal disk by a solid sub-cartilaginous frame, provided on the lower 

 surface of the disk with extensible tentacular cirri. The family 

 includes four genera ; namely, Vilella, the Holothuria of the Chinese, 

 which the reader will most readily comprehend from the brief 

 description we shall give of the Mediterranean Vilella ( V. limbosa 

 Fig. 93), which has been very minutely examined by M. Charles Yogt, 



