BBTOZOA. 135 



formation into the polype-form before they escape from the mouth of 

 the parent.* 



In the marine Hydrozoa the offspring developed in the ovicapsules 

 are, as a general rule, the ciliated larvae called " planulae : " the 

 Plumtdaria coronata offering an exception analogous to the Alcyo- 

 nella in the highest, and the Hydra in the lowest, class of polypes ; 

 whilst other Plumularue, the Corynidce, and certain species of Cam- 

 panularia deviate in a still more remarkable manner by the develop- 

 ment and liberation of the locomotive offspring in the guise of a 

 minute Medusa. 



We should be thus led from the Hydrozoa to the Acalephse if we 

 were guided solely by the phenomena of development ; but more 

 comprehensive views of the relations of the polype-shaped zoophytes 

 have conducted to higher types than that from which the Acalephae 

 seem to diverge, and, in the necessarily consecutive course of de- 

 scription, we now find ourselves, as at the conclusion of the discourses 

 on the Entozoa and Infusoria, compelled to retrace our steps and start 

 afresh from a lower level of the broad basis of the animal pyramid. 



Summary of the Classes, Orders, and Families of the Polypi of 

 Cuvier. 



Class HYDROZOA. 

 Tenlacles hollow, muricated with dart-ceUs or thread-cells. Sto- 

 mach without intestine, fixed in the parenchyme of the polype. 

 Polypary, when present, flexible, external. 



A. Naked, free, and solitary. Genus Hydra. 



B. Naked, or sheathed in a thin membrane, fixed and compound : 

 I tentacles claviform. Family Corysid.^. Genera, Coryne, Syn- 



coryne, Hydractinia, Corymorpha, Eleuthera. (These, like the 

 Hydra tuba of Dalyell, may be regarded as the procreating larvae 

 of Acalephje.) 



C. Protected by homy tubes, from the ends of which the polypes 

 emerge. Family TuBVLARiroM. Grenera, Tubularia, Ettdendrium^ 

 Pennaria. 



D. Protected by cells, developed according to regular patterns, from 

 a rooted and ramified horny tubular polypary. Spermatozoa and 

 locomotive progeny developed in external vesicles (sperm capsules 

 or ovicapsules), larger than the polype-ceUs. Family Sertv- 

 LARiiD^. Genera, Sertularia, Plumularia, Campanularia, &c. 



• CIX. voL ii. p. 209. 



