94 



MANUAL OF ZOOLOGY. 



In Velella (fig. 19, 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 gono- 

 blastidia, which resemble 

 polypites, and are termed 

 ' phyogemmaria ; ' and 

 3. the reproductive bo- 

 dies to which these last 

 give rise. The tentacles 

 are attached, quite inde- 

 pendently 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 anasto- 

 mosing system of canals, 

 which are ciliated, and 

 communicate with the 

 cavities of the phyogem- 

 maria and large central polypite." (Greene.) Velella is about 

 two inches in length by one and a half in height. It is of a 

 beautiful blue colour and semi-transparent, and it floats at the 

 surface of the sea, with its vertical crest exposed to the wind 

 as a sail. 



DIVISIONS OF THE PHYSOPHORID^:. (AFTER HUXLEY.) 



Fam. I. Apolemiada. Hydrosoma with nectocalyces and hydrophyllia, 

 the latter united with the other organs into groups which are arranged at 

 considerable intervals along the coenosarc. Ccenosarc filiform. Pneuma- 

 tocyst small. 



Fam. II. Stephana miada. Hydrosoma with nectocalyces and hydro- 



mfffifF 



Fig. 19. Physophorida. a Portuguese man-of- 

 war (Physalia utriculus), showing the fusiform 

 float and the polypites and tentacles (after Hux- 

 ley) ; b Velella vulgaris (after Gosse). 



