BOOK THIRD. 



ACALEPHAE. 



CLASSIFICATION. 



§ 53. 



The body of Acalephae is composed of a transparent, gelatinous sub- 

 stance, quite resembling the Corpus vitreum of the eyes of vertebrata. By 

 desiccation it almost entirely disappears, there remaining only a dry cel- 

 lular tissue, by which the form of the animal is imperfectly preserved. 

 These animals swim freely in the sea after having attained their develop- 

 ment. 



In the arrangement of their organs in ray-like processes radiating from 

 a common centre or a longitudinal axis, and where also is situated the 

 digestive apparatus, the quaternary system prevails. Copulatory organs 

 are always wanting. The classification is based, according to the system 

 of EschschoUz, upon difference of external form, and upon the structure of 

 their digestive and locomotive organs. 



ORDER I. SIPHONOPHORA. 



They take in their food by means of numerous tubes, which exist in 

 place of a stomach. Locomotion is aided, generally, by certain caililagi- 

 nous capsules. 



Family: Dipiiyidae. 

 Genera : Diphyes, Ersaea. 



Family : Physophoridae. 

 Genera : Physophora^ Stephanomia. 



Family: Piiysalidae. 

 Genus: Physalia. 



Family: Velellidae. 

 Genera \ RrJaria, Velella, Porpita. 



