108 HTDROZOA. 



particularly Physophora itself, two of the necto- 

 calycine canals, which coincide with what may be 

 termed the medial plane of the coenosarc, remain, 

 as usual, straight, while the two other, or lateral, 

 vessels become convoluted in a most complicated 

 manner before reaching the circular canal. As in 

 the Calycophoridce, the common cavity of each 

 nectocalyx is connected with that of the coenosarc 

 by means of a tubular pedicle. 



The hydrophyllia present variations both in 

 their structure, mode of attachment, and relations 

 to the other appendages. They may be either 

 foliaceous (Athorybia), or clavate {Apolemia), or 

 thick and wedge-like, or even pyramidal (Agal- 

 7na) ; while their surface is liable to be diversi- 

 fied with excavations and ridges, having smooth or 

 serrate lateral margins. Their arrangement is, 

 in general, more or less whorled. In Apolemia 

 they are proximal to all the other appendages, in 

 each separate group, and here, as in Halistemma 

 and Stephanomiay they become connected Avith 

 the coenosarc by more or less distinct peduLcles. 

 In Agahna, the attached apex of each is pierced 

 by a duct which terminates in a cascal phylloc3^st, 

 about the middle of the hydrophyllium, while its 

 opposite end opens into the somatic cavity. In 

 Forskalia the hydrophyllia are attached directly 

 to the peduncles of the polypites. The graceful 

 Athorybia rosacea possesses from twenty to forty 

 of these organs, inserted, in two or three circlets, 

 immediately below the pneumatocyst, and above a 

 much smaller number of polypites [Jig. 22, a). 

 In all other PhysopJioridcB with hydrophyllia, 

 nectocalyces also are present ; but Athorybia, 

 though destitute of the latter appendages, has the 



