CCELENTERATA : HYDROZOA. 93 



it doubtless acts as a buoy or "float" In the Portuguese 

 man-of-war (Physalia} the pneumatocyst communicates with 

 the exterior by means of an aperture in the ectoderm of the 

 pneumatophore. In Veklla and Porpita the pneumatocyst 

 communicates with the exterior by means of several openings 

 called " stigmata; " and from its distal surface depend numerous 

 slender processes, containing air, and known as "pneumatic 

 filaments." 



The polypites of the Physophoridce resemble those of the 

 Calycophoridcz in shape, but the tentacles have a much more 

 complicated structure, and are sometimes many feet in length, 

 as in Physalia. The " hydrophyllia" have essentially the same 

 structure as those of the former order. There occur also in 

 the Physophorida certain peculiar bodies, termed "hydrocysts" 

 or " feelers " ("fiihler" and " taster" of the Germans). These 

 resemble immature polypites in shape, consisting of a pro- 

 longation of both ectoderm and endoderm, usually with a 

 tentacle, and containing a diverticulum of the somatic cavity, 

 the distal extremity being closed, and furnished with numerous 

 large thread-cells. They are looked upon as " organs of pre- 

 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-swim- 

 ming medusoids. In many of the Physophoridcz the male and 

 female gonophores differ from one another in form and size, 

 and they are then termed respectively " androphores " and 

 " gynophores. " As regard s their development the Physophorida 

 obey the same general law as the Calycophorida. 



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 cceno- 

 sarc bears a double row of nectocalyces, which are channeled 

 on their inner faces to allow of their attachment to the cceno- 

 sarc. 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 (fig. 19, 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. 



