188 LECTURE IX. 



sembles, but never becomes, a Polygastrian, a Rotifer, a Hydrozoon 

 and an Anthozoon. 



The Cyancea aurita is, however, but the representative of one 

 of the three leading divisions of the remarkable animals grouped 

 together under the name of Acalephce. With regard to the develop- 

 ment of the ciliograde and physograde species, scarcely anything 

 connected or precise is at present known. The Medical Officer 

 who may be destined for foreign service, and to whom the study 

 of Nature offers any charm, could hardly contribute observations 

 more valuable to natural history than such as he might be able to 

 make on the generation and development of the Pelagic Acalephaj. 



Summary of the Orders and Families of the 



Class ACALEPH^. 

 Free swimming marine animals of a gelatinous or membranous 

 tissue with thread-cells. Digestive cavities or canals adherent 

 to the surrounding tissues, and communicating with a more or less 

 ramified chylaqueous system. Most are dioecious, and pass by 

 metagenesis through the forms of the monad and the polype, before 

 acquiring the sexual acalephoid character. 



Order PULMOGRADA. (Medusa.) 

 Body discoid, with a marginal velum, and a central inferior 

 mouth, usually pi'olonged into a more or less complex proboscis. 

 Locomotion by rythmical contractions of the disc. Sexes distinct. 



Suborder Gymnophthalmata. (Bare-eyed Medusfe.) 

 Cysticles unprotected : Chylaqueous canals simple, or, if ramified, 

 not anastomotic. Gemmiparous. (Some are probably larvae.) 



Families Sarsiidm. Chylaqueous canals simple, four : ovaries 



in the substance of the proboscis. 

 Genera: Sarsia, Euphysa^ Steen- 

 strupia. 



Geryoniid^. Chylaqueous canals simple, four : ovaries 



beneath the disc. Genera Geryoina, 

 Thaumantias, Slahberia. 



CiRCEiDM. Chylaqueous canals simple, eight: 



ovaries eight, beneath the disc. 

 Genus Circe. 



^qvore/DjE. Chylaqueous canals simple, eight or 



more : ovaries linear on the course 

 of the canals beneath the disc. 

 Genera Polyxenia, Stomotrachiuw, 

 JEquoria, Phorcunia. 



