114 THE OCEANIC HYDROZOA. 



The inner surface has a deep-yellow colour, and the conical manubrium or polypite presents 

 four reddish-brown lateral enlargements, which are the sexual organs. 



From the common cavity at the base of the manubrium sixteen radial canals arise, 

 and pass to a circular vessel surrounding the edge of the calyx. 



On the surface of the calyx there are sixteen radiating rows of thread-cells, one 

 corresponding with each longitudinal canal. Where the latter opens into the circular canal 

 there is a semicircular dilatation, containing externally a whitish body, formed of vesicles like 

 drops of oil, the larger of which are coloured brown, red, or violet. The valvular membrane 

 lies within these enlargements, and is seen with difficulty. There are neither litliocysts nor 

 ocelli. 



Only one of Gegenbaur's specimens possessed a tentacle, and that was single. It 

 arose by a broad base from one of the enlargements just described, and attained a length of 

 half a line, ending below in a knob with a depressed centre. 



The yellow colour of the inner surface of the calyx is produced by yellow cells, which 

 form close networks between the longitudinal canals. Two of the specimens observed were 

 male, and one female, but the sexual products were in none fully developed. 



Of the earliest stages of the development of Velella nothing is known, but a very 

 young form (younger than almost any hitherto observed') is depicted in PL XI, fig. 9. The 

 animal was not one tenth of an inch long, and the horizontal disc of the adult was 

 represented by a bell-shaped, membranous expansion, continued above into a broad crest, half 

 as high as the whole depth of the animal. It was symmetrically disposed, and, its 

 superior edge, far from being pointed, was rather concave, and in the centre presented a 

 curious thickening. 



The central polypite was already open at its distal extremity, and around its base 

 were a few short, csecal processes, the rudiments of the gonoblastidia or of the tentacles. 

 The margin of the disc was occupied by a single series of large, oval vesicles. 



The somatic cavity was divided by a series of vertical septa, which passed con- 

 tinuously over the pneumatocyst into the crest, near whose free edge they terminated 

 abruptly. At their other ends, or near the margin of the disc, they also ended abruptly, 

 and between them other very short septa were interposed. The somatic cavity and its 

 continuation into the crest were thus broken up into a seiies of parallel canals, united at 

 their ends by two marginal canals (/>,/>) at right angles with one another, one in the 

 disc, the other in the crest. The canals were ciliated, and I could observe granules 

 passing from one into the other. 



The pneumatocyst shone through the disc, and did not extend into the crest at 

 all. By carefully tearing away the fleshy substance with needles, I succeeded in isolating it 

 (iig. 10). It then appeared as an almost hemispherical body, convex above, and flat below. 



1 Eschscholz's RataruE, rightly suspected by De Blainville to be young Velella, are said to 

 have been a line long. Those observed by M. Vogt's friend (Vogt, 1. c., p. 83) were five millimetres 

 (one fifth of an inch) long, and were evidently much further advanced. The smallest Velellee observed 

 by Kolliker were three or four lines long, and differed in no essential respect from the adult except 

 that they were more "Rataria-\\V.e" possessed no medusoid buds, and exhibited a smaller number of 

 " small polypes," tentacles, and chambers in the pneumatocyst. 



