HARDWICKE'S SCIENCE-GOSSIP. 



63 



thing equally water-tight, and arrived there place it 

 at once in a jar of water. Here you must leave it 

 for a few hours, at the end of which you will have 

 the pleasure of seeing in the place of those little 

 green balls a narrow cylindrical animal, rayed at one 

 end with from six to ten tentacles. As you watch, 

 maybe a little Cyclops, or water-flea, comes flitting 

 by ; instantly one or more of those tentacles close 

 round it, and then force it unresistingly into an 

 orifice in the centre of the rays. You have seen a 

 Hydra viridis catch and eat its unwary prey. And 

 now, with the animal in front of us to refer to on all 



power is provided; by the process of gradually 

 changing the position of the suctorial foot. You 

 may have the pleasure of seeing it slowly creep up 

 the side of the glass vessel and launch off along the 

 the surface of the water, the sucker -like foot project- 

 ing a little above, and the body dependent under- 

 neath, as is usual with it. Under a lens we perceive 

 that there is an opening amid the restless arms, lead- 

 ing into a cavity. The tentacula are placed rather 

 lower than this mouth, which is protruded a little in 

 the form of a snout (hypostome or oral cone). The 

 body cavity is wide at the commencement, and from 



Fig. 57. — 1. H. viridis, greatly magnified. 2. H. viridis, showing a, spermatic capsules (wall organs), and B, ovarian capsule 

 (female ditto). 3. Portion of more magnified, and showing a, nematocysts (in situ). 4. Young Hydra bursting from ovum. 

 5. Hydras on Duckweed (nat. size). 6. Stinging capsules. 7. Ditto, in size. 8. Ditto, exerted. 



points, we will proceed to consider its structure and 

 economy, not a dry subject by any means. My 

 classical readers will no doubt remember the dragon 

 of the Lernean marshes in Argolis, which Hercules 

 ■was sent to kill. As fast as he struck off one of its 

 heads, two sprang up in its place. This dragon was 

 called Hydra, and from it our little animal takes its 

 generic name. The specific, viridis, of course ex- 

 plains itself. If we examine the extended animal 

 closely, we shall see that it is about half-an-inch long, 

 and is apparently fixed to the leaf or stem by its base. 

 It is not, however, perma?iently fixed. Locomotive 



it a narrow canal runs to the base. You look for an 

 opening at the posterior end in vain. " What ! " 

 you say, "how does the creature rid itself of its 

 digested food ? " Oh, a simple matter enough ; it 

 uses its mouth as an anus ; an unusual proceeding, I 

 grant you, but nevertheless a fact. There have been 

 some who have tried to prove the existence of a true 

 anus, but their efforts and statements have not been 

 confirmed. The sides of its body appear smooth 

 when the creature is fully extended, but when only 

 partly so the skin seems to wrinkle, conveying to the 

 eye a crenulated appearance. The tentacula which 



