102 



HYDHOZOA. 



and, the free extremity of the pneumatophore 

 being likewise perforate, a communication exists, 

 in these genera, between the cavity of the pneuma- 

 tocyst and the surrounding medium. In Rhi 



nzo 



branched 



ith of 



freely depend from the distal surface of the pneu- 

 matocyst. Each process consists of a layer of the 

 investing endoderm containing in its axis clear cel- 

 lseform bodies, 02 of an inch long, each of which 

 includes an opaque oval endoplast, about 

 these dimensions, and this, in its turn, a more mi- 

 nute particle or nucleolus, oval or circular in form, 

 and -0008th of an inch in diameter. In Agalma 

 and Forskalia radiating membranous partitions 

 connect the walls of the pneumatophore with those 

 of the pneumatocyst, below which each terminates 

 in a free arcuated edge. In Velella and Porpita 

 the pneumatocyst is furnished with several open- 

 ings, or stigmata, communicating with the exterior, 

 while to its distal surface are attached a number 

 of long slender processes enclosing air, and hence 

 termed the * pneumatic filaments.' 



Excepting the presence of the pneumatophore 

 and the absence of a somatocyst, the general plan 

 of structure in these Hyclrozoa differs little from 

 that of the Galycophoridce. In Apolemia, as in 

 Diphyes, the numerous groups of appendages are 

 supported at intervals along a slender, unbranched, 

 connecting stem. Physophora, the type of the 

 order, has a filiform, but comparatively short, cce- 

 nosarc, terminated proximally by a pneumato- 

 phore of moderate size, below which the greater 

 portion of its length is occupied by a double 

 series of nectocalyces, each alternating with its 

 successor on the opposite side, and deeply grooved 



' 





