ANTIIOZOA IIYDROIDA. 11 



cavatecl as it were in the Lody, " neither figured nor Hmited 

 by particular membranes," and from which the indigestible 

 remains of the food are ejected at the same aperture by which 

 it had entered. The part of the body underneath the stomach 

 offers no peculiarity in structure, and although it rests upon a 

 sort of diaphragm in the cell, it is nevertheless continuous 

 with the more fluid pulp that fills the branches and stem of 

 the polypidom ; and by this means all the polypes of it are 

 connected together by a living thread, and made to constitute 

 a family whose objects and interests are identical, and whose 

 workings are all regulated by one harmonious instinct. This 

 organic connection and harmony between the individuals has 

 led Linnseus and Cuvier to regard the whole composure as one 

 animal furnished with a multitude of armed heads and mouths; 

 and it would have been difficult to controvert the opinion, had 

 our knowledge been limited to those species only which ramify 

 after the manner of a tree : but the contrary view which we 

 have taken is supported by the evidence of those species which 

 are simple and separate of themselves, and of those others 

 which, although compound, have yet a defined and limited 

 digestive organ, as is the case in the genera Ooryne and Hy- 

 dractinia.* 



In these simple animals there is no nervous system, -j- and 

 no organ of sense in the adult ; no organ exclusively appro- 

 priated to the function of respiration, no circulatory system, 

 nor any vessels for carrying the digested products of the 

 stomach into and throughout the body. All seem to be con- 

 fused and combined ; and the water in which the polypes live, 

 in its flow over the external surfaces, and in its penetration 

 into the stomachal cavity, suffices to impart the oxygen 

 necessary to complete the assimilation of the nutritive liquid, 

 that oozes from its source directly into the parenchyma of the 

 body with which it enters into combination. There is, how- 

 ever, a kind of circulation in the species with a polypidom, 



* Van Beneden, Recher. des Tubulaires, p. 1 9. 



t " But as we perceive, in these animals, phenomena which take place by the 

 medium of nerves in animals of a more elevated order, that is to saj', sensibility and 

 voluntary motion, it is not improbable that in them the nervous substance is mixed 

 with their gelatinous or mucous mass, without being demonstrable as a particular 

 tissue." — Tiedemann's Comp. Phys. p. G4. See also Macleay's Hor. Ent. p. 196. 



