332 Natural History of British Zoophytes. 



or mouth which leads into a wider cavity excavated as it were in the 

 midst of the jelly,* and from which a narrow canal is continued down 

 to the sucker. When contracted, and also when fully extended, the 

 body appears smooth and even, but " in its middle degree of exten- 

 sion," the sides seem to be minutely crenulated, an effect probably of 

 a wrinkling of the surface, although from this appearance Baker has 

 concluded that the Hydra is annulose, or made up of a number of 

 rings capable of being folded together or evolved, and hence, in some 

 measure, its extraordinary ability of extending and contracting its 

 parts.-(- That this view of the Hydra's structure is erroneous, Tremb- 

 ley has proved ;% and the explanation it afforded of the animal's con- 

 tractility was obviously unsatisfactory, for it was never pretended that 

 such an anatomy could be detected in the tentacula, which, however, 

 are equally or more contractile. These organs encircle the mouth 

 and radiate in a star-like fashion, but they seem to originate a little 

 under the lip, for the mouth is often protruded like a kind of small 

 snout : they are cylindrical, linear or very slightly tapered, hollow 

 and roughened, at short and regular intervals, with whorls of tuber- 

 cles which, under the miscroscope, form a very beautiful and interest- 

 ing object ; and I have thought, when viewing them, that every lit- 

 tle tubercle might be a cup or sucker similar to those which garnish 

 the arms of the cuttle-fish. § Trembley has shewn us that this is a 

 deception, and that there is really no exactness in the comparison. \\ 



* Pallas denies this. " Ab alimento recepto cavatce, inquam, baud enim Hy- 

 dras corpus naturaliter intestini instar cavum credidevim. Totum solidum et 

 medullare, pro admoto alimento, cerae instar, digitim admittentis, cavari eoncipio 

 parenchyma et alimentis insinuatis sese circumfundere. Qui alias per longi- 

 tudinem dissecta Hydra, illico qualibet portione deglutire, et cavo clauso alimen- 

 ta condere posset? quod tamen observare rarum non est." Elench. Zooph. 27, 

 28. — For a view of the Hydra's stomach see Tremb. Mem. pi. 4, fig. 7, co- 

 pied by Roget in bis Bridgew. Treat, ii. 74. fig. 241. 



-f- " The outward coat is white like the arms, and made up of minute annuli 

 or ringlets, that double in the midst, and can, occasionally, be folded close to- 

 gether, in the manner of a paper lanthorn." — Hist, of the Polype, 25. 



\ Mem. 27. 



§ Pallas has the same suggestion. Elench. 26. See also Roget's Bridgew. 



Treat, i. .182 Baker says that " two or three pretty long hairs" issue from each 



of the papillae or tubercles, p. 36. ; and Trembly has figured a short hair issuing 

 from some of them, Mem. 62, pi. 5, fig. 3. This appearance of hairs is, I pre- 

 sume, produced by the glutinous secretion from them being drawn out into fine 

 lines and drying on the glass. The tentacula probably adhere to foreign bodies 

 principally by means of a mucous excretion, and being as it were engrained into 

 the microscopic interstices of the body to which they are applied. — Tremb. 

 Mem. 46. 



II Mem. 108. 



