110 CLASS III. 



greater part of them have no connexion with these canals, or with 

 the central polyp, but lateral branches of the vessels open into their 

 pedicles, so that they at once give the product of digestion to the 

 vascular system. In Porpita the lesser polyps open into liver-canals 

 and not into vessels. 



The generative organs are seated, as clusters of minute bodies, on 

 the pedicles of the smaller polyps. They become transparent and 

 pyramidal, and having gradually assumed the medusan form are 

 detached. They were first noticed by DELLE CHIAJE, Descriz. iv. 

 p. 107, Tav. 146, fig. 10, 12. The sexual germs are formed on the 

 wall of the radiating vessels. HUXLEY, GEGENBAUER, 1. 1. 



The prehensive organs are placed around the lesser polyps on the 

 horizontal margin of the mantle. They are hollow and open into a 

 vessel like the lesser polyps. They have no special nettle-nodes, but 

 numerous scattered thread-cells. 



The air-canals were discovered by KROHN ; they are minute vessels 

 which pass from the innermost air-spaces of the horizontal cartilage, 

 perforate the mass of the liver, and reach the walls of the polyps 

 where they appear to terminate by closed extremities. They are 

 most numerous in Porpita. See KOELLIKER Die Siphonoph. pp. 46 

 64.] 



Velella LAM. A semi-orbicular crest, compressed, containing a 

 cartilage within, placed obliquely albove the disc. Marginal ten- 

 tacles simple. 



Sp. Velella spirans, Medusa velella L., Holoth. spirans FORSK. Icon. Rer. 

 nalur. Tab. xxvi. fig. k, Armenistarium velella COSTA Ann. des Sc. nat. 

 sec. se'rie, Tom. XVI. PI. 13, fig. 3, (figure of the vessels from the stomachs 

 on the inferior surface of the cartilaginous disc), in the Mediterranean. 

 According to FORSKAL the French sailors call the animal Vallette: they 

 eat it fried with flour and butter. The name Velella appears to be derived 

 from velum and from the crest, which like a full-spread sail, adorns the 

 upper surface. The beautiful blue colour of the animal is imparted to the 

 water in which it is examined, but disappears in spirit of wine. During 

 life the creature is not unattractive ("non invenusta est quantum vermi 

 licet," FORSK. Descr. Animal, p. 105) ; see the coloured figure of LESUEUR 

 in PERON, Voyage aux terres austr. PI. xxx. fig. 6. (This species is from the 

 Tropical Seas, Velella scaphidia PERON). For the other species, not easily 

 to be distinguished, of this genus, consult chiefly ESCHSCHOLTZ Syst. der 

 Acalephen, s. 168 175. 



Subgen. Rataria ESCHSCH. Crest membranous, placed longitudi- 

 nally on the disc. 



