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CCELENTEEATA : HTDEOZOA. 83 



tentacle, and containing a diverticulum of the somatic cavity, 

 the distal extremity being closed, and furnished with nume- 

 rous large thread-cells. They are looked upon as * organs of 

 prehension and touch,' and they are somewhat analogous to 

 the * nematophores ' of some of the Sertularida. 



As regards the reproductive organs, they are developed 

 upon special processes or ' gonoblastidia,' and they may re- 

 main permanently attached, or they may be thrown off as 

 free-swimming medusoids. In many of the PhysopJwridce the 

 male and female gonophores differ from one another in form 

 and size, and they are then termed respectively ' androphores ' 

 and ' gynophores.' As regards their development the Physo- 

 phoridce obey the same general law as the Galycophoridce. 



.In PhysopJiora the hydrosoma consists of a filiform cceno- 

 sarc, which bears the polypites and their appendages, and 

 dilates proximally into a pneumatophore. Below this point 

 the ccenosarc bears a double row of nectocalyces, which are 

 channelled on their inner faces to allow of their attachment to 

 the ccenosarc. There are no hydrophyllia, but there is a series 

 of ' hydrocysts ' on the proximal side of the polypites. 



Physalia, or the Portuguese man-of-war, is composed of a 

 large, bladder-like, fusiform ' float ' or pneumatophore 

 sometimes from eight to nine inches in length upon the 

 under surface of which are arranged a number of polypites, 

 together with highly contractile tentacles of great length, 

 4 hydrocysts,' and reproductive organs. Physalia is of com- 

 mon occurrence, floating at the surface of tropical seas. 



In Velella the hydrosoma consists of a widely expanded 

 pneumatophore of a rhomboidal shape, carrying upon its upper 

 surface a diagonal vertical crest. Both the horizontal disc 

 and the vertical crest are composed of a soft marginal 'limb,' 

 and a central more consistent ' firm part. ' ' To the distal sur- 

 face of the firm part of the disc are attached the several ap- 

 pendages, including, 1. a single large polypite, nearly central 

 in position ; 2. numerous small gonoblastidia, which resemble 

 polypites, and are termed " phyogemmaria ; " and 3. there- 

 productive bodies to which these last give rise. The tentacles 

 are attached, quite independently of the polypites, in a single 

 series along the line where the firm part and Hmb of the disc 

 unite. There are no hydrocysts, nectocalyces, or hydrophyllia. 

 On all sides the limb is traversed by an ana- 

 stomosing system of canals, which are ciliated, and com- 

 municate with the cavities of the phyogemmaria and large 

 central polypite.' (Greene.) Velella is about two inches in 

 length by one and a half in height. It is of a beautiful blue 



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