IOS MANUAL OF ZOOLOGY. 



cavity, the distal extremity being closed, and furnished with 

 numerous 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 Sertnlarida. 



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 Physophorida 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 Calyco- 

 phoridce. 



In Physophora the hydrosoma consists of a filiform ccenosarc. 

 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 poly- 

 pites. 



Physalia, or the Portuguese man-of-war (fig. 29, 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. 29, 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 hydrophyllia. . . . 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 



