Introduction to Animal Morphology. 99 



expanded into a variously shaped pneumatophore, 

 containing at its apex a chitinous air-sac (pneumato- 

 cyst), which does not communicate with the cavity of 

 the pneumatophore, or with the, somatic cavity, but 

 opens externally by a pore or stigma (except in 

 Physophora, Forskalia, Agalma, Athorybia, and 

 Halistemma), and is held in its place by a reflection 

 of the endoderm. Its shape may be spheroidal 

 (Athorybia), oval (Physophora), cylindrical and small 



Ima;, <5cc. The hydrophyllia and tentacles are as 

 in Calycophorida? ; and there are also, on the ccenosarc, 



:ysts, polypoid, protective, or prehensile processes 

 of endo- and ectoderm, each with one long, filiform 

 tentacle, closed distally, and profusely armed with 

 trichocysts. The tentacles may be simple ccecal 

 tubes with vacuolated endoderm (Velella), or branched 

 at the end (Porpita). Each may be at the base of a 

 ite (Apolemia), or projecting from the ccenosarc 



endently of the polypites, each with a basal sac 



-alia ;. In Physophora, the tentacle has a large, 

 spheroidal involucre enclosing the sacculus. From 

 the air-sac to the wall of the pneumatophore, septiform 

 processes pass in I-'orskalia and Agalma. In Velella, 

 slender, jointed, air-holding processes project from 

 rnatocyst into the wall of the hepatic or^an 



matic filaments". In Rhizophysa, IOIILT, branched, 

 cellular processes, covn-d l>y ciliated endoderm, pro- 

 ;he wall <>f the pneumatocyst into the cavity 

 of til-- . perhaps like the hepatic o 



11*. 



medusiform buds form on Ma^tnsi \ 1,-s, aiid 

 ; malfs androphon-s and fcinal- 



nay co-exist, orb ite. 



usually unilateral. 



II 2 



