HYDRA. 77 



port ant and still more interesting points, though sufficiently acquainted 

 with them. I believe now that it would have been better had I done diffe- 

 rently, for it would have prevented certain authors from betraying them- 

 selves into very erroneous conclusions of the import of my observations. 



I shall resume the subject more at large in this place, viewing the 

 hydra, in the first instance, as a perfect animal. 



The body of the Hydra tuba is a hollow cone five lines in length, 

 thick and fleshy. Thirty or more very extensile, flexible, fine slender 

 muricate tentacula descend twenty-one lines from the margin, collectively 

 forming a beautiful silken-like pencil waving amidst the water. The 

 mouth rises as a conic frustum among them, in the centre of the disc, 

 much resembling the closed mouth of the Actinia ; but there is no analogy 

 to a proboscidal organ, either here or in any other of the hydraoid race. 

 The natural colour of the animal is universally dingy white, sometimes 

 faint orange, perhaps according to the season, but it is specially affected 

 by the quality of the food. It is affixed by the apex ; and is exclusively 

 an inhabitant of the sea. — PI. XIII. fig. 1. 



Throughout there is a strong analogy in many prominent features of 

 this animal to the nature of the Actinia. 



Complete developement of all the parts of the Hydra tuba is best 

 exposed under temporary abstinence : the observer will be disappointed 

 of seeing them if resorting to his specimen in a state of repletion. While in 

 abstinence, the animal remains suspended by the apex, the body lengthens, 

 and the tentacula are extended to the utmost stretch in quest of prey. 

 If sensible of its presence when inaccessible, the hydra does not em- 

 ploy them as instruments of capture in sweeping around, but the mouth 

 widely dilating, projects the edge as a thin flexible lip in much action. 

 Now, the capacious cavity of the stomach indistinctly exposes a kind of 

 columnar range around the internal parietes, possibly corresponding with 

 the external form of the body, at times bearing faint resemblance to a 

 cluster column. Exposure so complete is very rare. The stomach is most 

 capacious : when coloured food gorges the hydra, it is seen nearly at the 

 apex ; indeed, excessive distension seems to detach the animal from its 

 point of adhesion, when it falls to the bottom of its vessel. 



