DISCOPHORA. 41 



ACALEPHA. 



Animals of radiate structure, of pellucid gela- 

 tinous substance, swimming freely in the sea, after 

 they have attained their adult condition ; with a 

 digestive cavity, whence vessels diverge, carrying 

 a circulating nutritive fluid ; furnished with various 

 organs of sense, and with poisoning weapons simi- 

 lar to those of the Zoophyta : increasing generally 

 by eggs; and subject to metamorphosis. 



Body in form of a circular disk, 

 more or less convex, and umbrella- 

 like, with a great central digestive 

 cavity ; moving by alternate con- 

 tractions and expansions of the disk. Discopfrora. 



Body symmetrical, not disk- 

 shaped, with a great central diges- 

 tive cavity ; moving by means of 

 many parallel rows of cilia, set in 

 longitudinal lines on the surface. . Ctenophora. 



Body irregular ; without a central 

 cavity for digestion ; with sucking 

 organs ; moving by means of a con- 

 tractile cavity, or by vesicles filled 

 with air Siphonophora. 



Order I. DISCOPHORA. 



Eye-specks uncovered, or wanting ; 

 circulating vessels proceeding to the 

 margin quite simple or branched. . Gymnophthahnata. 



Eye-specks protected by membra- 

 nous hoods or lobed coverings ; cir- 

 culating vessels much ramified, and 

 united into a network Steganophthalmata. 



