SC7PHOZOA 



125 



Fig. 208 



FAMILY DIPHYIDAE. 



Two neetophores present: 10 genera and about 35 species. 



DIPHYES Cuvier. Neetophores conical and very large; the remain- 

 der of colony can be retracted into a groove in the neetophores and is 

 constantly being shortened by the breaking off of 

 the terminal and oldest groups of individuals, each 

 group (which is called an Eudoxia) thus separated 

 leading an independent life and becoming sexually 

 mature: 6 species. 



D. bipartita Costa (Fig. 208). Total length 30 

 mm. ; length of the neetophores 10 mm. ; body trans- 

 parent: tropical and subtropical Atlantic; Mediter- 

 ranean; occasionally on New England coast; often 

 very common. 



CLASS 2. SCYPHOZOA. (SCYPHOMEDUSAE.) 



These animals have usually an alternation of 

 generations, in a few (Pelagia), however, the medu- 

 soid generation and in others (Lucernaria) the 

 hydroid alone being present. The medusoid plays 

 a much more conspicuous part than the hydroid. 

 The latter is a small, usually non-colonial animal 

 called the scyphistoma, which is less than a centimeter in height and 

 resembles the fresh-water Hydra in appearance (Fig. 217, A). It differs 

 from Hydra, however, in that the aboral end is fixed to the bottom in a 

 cup formed of the perisarc, in the possession of four longitudinal folds 

 of the entoderm called mesenteries which project into the gastrovascular 

 space and of an ectodermal gullet. The scyphistoma is an asexual 

 animal and reproduces by budding exclusively. New scyphistomas may 

 be produced by a process of lateral budding from stolons sent off from 

 the foot. The medusoid generation is produced by a process of terminal 

 budding called strobilation (Fig. 217, B). The scyphistoma grows in 

 height and a series of constrictions appear which divide it into a number 

 of discs. Each disc is called an ephyra (Fig. 217, C) and is a young 

 medusa or jellyfish, which on becoming free grows in time to be a sexual 

 animal. 



The medusa which is thus produced is often a large animal; Cyanea 

 may be two meters and more in diameter with tentacles thirty-five 

 meters or more long. It is called acraspedote because the velum, which 

 is so characteristic of the craspedote Hydromedusae, is wanting or 

 rudimentary. The periphery of the bell is lobed or scalloped and may 

 or may not have tentacles. The manubrium is sometimes very long and 



Diphyes bipartita 

 (Har 



targitt). 



