98 MANUAL OF ZOOLOGY. 



hension 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 remain 

 permanently attached, or they may be thrown off as free- 

 swimming medusoids. In many of the Physophoridce the 

 male and female gonophores differ from one another in form 

 and size, and they are then termed respectively " andro- 

 phores " and " gynophores." As regards their development, 

 the Physophoridce obey the same general law as the Caly- 

 cophoridcB. 



In Physophora the hydrosoma consists of a filiform ccenosarc, 

 which bears the poljrpites 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 poly- 

 pites. 



Physalia, or the Portuguese man-of-war (fig. 20, a), is com- 

 posed of a large, bladder-like, fusiform " float" or pneumato- 

 phore — 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, " hy- 

 drocysts," and reproductive organs. Physalia is of common 

 occurrence, floating at the surface of tropical seas ; and fleets 

 of it are not uncommonly driven upon our own shores. 



In Velella (fig. 20, b) 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 surface of the firm part of the disc are attached 

 the several appendages, including, i. a single large polypite, . 

 nearly central in position; 2. numerous small gonoblastidia, 

 which resemble polypites, and are termed " phyogemmaria ; " 

 and, 3. the reproductive bodies to which these last give rise. 

 The tentacles are attached, quite independently of the poly- 

 pites, in a single series along the line where the firm part and 

 limb of the disc unite. There are no hydrocysts, nectocalyces, 

 or hydrophyUia. ... On all sides the limb is traversed 

 by an anastomosing system of canals, which are ciliated, and 

 communicate 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 



