HYDROZOA. 



103 



on its inner face for attachment to the ccenosarc, 



(fig 



The distal extremity of the latter 



forms an expanded bulb, above which are disposed, 

 in a spiral or circular manner, the various appen- 

 dages; consisting of polypites, tentacles, hydrocysts, 

 and organs of reproduction. Of these the hydro- 

 cysts are uppermost, or external ; next come the 

 polypites, with a tentacle at the base of each, 

 between, or above, which the gonophores, of both 

 sexes, are arranged. The usual length of Physo- 

 phora is about two inches. 



The typical genus just described may advan- 

 tageously be contrasted, on the one hand, with 

 such forms as Apolemia or Halistemma, on the 

 other, with the widely different, though equally 

 aberrant, genera, Porpita and Velella. 



In Halistemma rubrum the appendages are 

 attached to a thread-like stem, nearly forty 

 inches in length, having a float of only three or 

 four lines in its longest diameter, close beneath 

 which the swimming-bells, about sixty in number, 

 extend in two parallel rows for a distance of six 

 or seven inches. The remainder of the coenosarc 

 is occupied by the polypites, tentacles, hydrocysts, 

 bracts, and reproductive buds, all associated in one 

 continuous series. Especially conspicuous, from 

 their bright vermilion hue, appear the complex ten- 

 tacular sacculi, while fainter longitudinal bands of 

 the same colour mark the hepatic striae of the 

 polypites, whose size, in this genus, is considerable. 

 The general aspect of this most beautiful, yet 

 withal, extraordinary being, has been compared 

 by Vogt, its discoverer, to that of a delicate, trans- 

 parent garland of flowers, endowed, in a marvel- 

 lous manner, with life and activity. 



H 4 



