334 



HYDEOID^. 



Part IV. 



Eysenhardt; the Phy.saliiv, as limited by Lesson;^ the Phy,sophora3 of Goldfuss, exdud- 

 ing Physalia (Arethusa) ; and the Diphyog of Cuvier. These sub-orders may be 

 characterized as follows : — 



1. PorpitEe Golclf. — The commmaity of these Acalephs buds from a primary 

 hydra, which is provided with many tentacles, and retains its individuality. The 

 secondary hydrse arise between the tentacles of the primary liydi'a and its proboscis ; 

 they are small, club-shaped, and without tentacles. From these small hydrae arise 

 medusae-buds, which are cast off and become free sexual Medusa?, long known 

 under the name of Linuche, and recently described anew as Chrysomitra. 



2. Physalia? Less.^ — Physalia starts from a jDrimitive hydra, which attains 

 gigantic dimensions, and, losing its individuality, becomes a floating apparatus for the 

 whole community. The secondary hydrte all arise from one and the same side of 

 the primitive hydra, in bunches ; they vary in size and development from one 

 another, some being closed at the actinal end, while others have a gaping mouth ; 

 some hAve one long, lateral tentacle, starting from their base, and attached to their 

 side, and others none. By the side of these arise large bunches of small, fertile 

 medusae-buds, with four radiating chymiferous tubes and a circular tube, but without 

 tentacles. These Meduste wither upon the stock from which they arise. The 

 mode of combination of the hydrte and medusce, in different species of this type, 

 may afford generic characters to subdivide them. 



3. Physophora? Gohlf? — Community budding around a slender tentaculated 

 hydra, the abactinal end of which terminates in an air cyst. From the abactinal 

 sides of this primary, egg-born hydra, arise sterile sessile medusa?, without tentacles 

 and proboscis, arranged in two or more vertical rows ; and from the actinal side, 

 one or two kinds of secondary hydrJB, with or without compound or simjile ten- 

 tacles. Between the secondary hydra?, small sessile male and female Medusae bud 



' Lesson is the first author \\lio has isolated 

 the Physalias, as a separate group, from all other 

 Acalephs. He considers them only as a family, 

 but they really constitute a distinct sub-order. 

 Leuckart, Quatrefages, and Huxley, have published 

 the most recent accounts upon this type. See 

 their papers, quoted above. The way in which 

 MeCrady has divided the Siphonophonv, and his 

 attempt to incorporate them in one and the same 

 sub-order with the Tubularians, does not seem to me 

 to be justifiable. In the first place, the mode of 

 growth of his Endostomata and Exostomata is not 

 so characteristic as he supposes, as a comparison 



of the meduste-buds of Coryne and Obelia. de- 

 scribed above, pp. 102 and 318, may show. In the 

 second place, the Diphyidte arise in a totally different 

 manner from the other Siphonophora>, as the obser- 

 vations of Gegenbaur upon the reproduction of 

 Diphyes have shown. Their community is not 

 built up from a hydra, but from a medusa. Again, 

 the primitive hydra of the Siphnnophora; is never 

 pedunculated ; that of the Tubularians always is. 



^ For this type, see the papers and works of 

 Kolliker, Leuckart, Vogt, Gegenbaur, and Huxley, 

 quoted above. Vol. III. p. 27 ; also Chapter II. 

 Vol. IIL p. 73. 



