By accident two small Water Fleas were imprisoned with the polyp, and one (a shrimp-like looking creature, carrying behind her a great bag of eggs) came into contact with the tentacles, and seemed paralysed for a time. The hydra made no attempt to convey the captive to its mouth, but held it tight until another Water Flea, a round merry little fellow (Chydorus sphæricus), came to the rescue, and assisted Canthocamptus to escape by tugging at her tail. This friendly action may not have been prompted by the intelligence which seemed to suggest it, but those who have kept tame soldier-crabs and prawns in an aquarium, will not be indisposed to attribute to the crustaceans more brains than they have usually credit for. It must, however, be confessed that the subsequent conduct of Mrs. Canthocamptus did not indicate the possession of much prudence, for she learnt no lesson from experience, but repeatedly swam against her enemy's tentacles, suffered many captures, and only escaped being devoured through the indifference, or want of appetite, which the polyp evinced.
A, Canthocamptus minutus; B, Chydorus sphæricus; C and D, Capsules and poison-thread of polyp; E, Tricodina pediculus, side view and under view; F, Kerona polyporum.—Microg. Dict.
On the body of the Canthocamptus were some small transparent vases or bottles, containing living objects, which sprang up and down. These were members of the Vorticella family, called Cothurnia, and will be hereafter described.
Hydra viridis, in various shapes.
Watching the hydra it was curious to note the changes of form which these creatures are able to assume. Now the tentacles were short and thick, and the body squat; now the body was elongated, like the stem of a palm tree, and the tentacles hung gracefully from the top. From some of the polyps little round buds were growing, while other buds were already developed into miniature copies of the parent, and only attached by a slender stalk. In a few days many of these left the maternal side, fixed their own little tails to the glass, and commenced housekeeping on their own account.
Polyps may be obtained at all times of the year by bringing home duckweed, conferva, and other water-plants from the ponds. Some hauls may be unsuccessful, but if one pond is not propitious others should be tried. The plants should be put in a capacious vessel of water, and placed in the light, where, if polyps be present, they will show themselves within twenty-four hours, either attached to the sides of the glass, or hanging from the plants, or suspended head downwards from the upper film of the water. They are elegant objects, and may be kept without difficulty for some weeks. After being confined in a small quantity of water for purposes of examination, they should be carefully replaced in the larger vessel, and may thus be used again and again without suffering any injury. A low power—a three or two-inch glass—or a one-inch, reduced by employing the erector—is the most convenient for examining the whole creature, but higher powers are necessary to make out its minute structure. They should be viewed with direct and oblique light, as transparent and also as opaque objects. In the latter case the "Lieberkuhn," or polished silver speculum, is convenient, and if the microscope is not furnished with Lister's dark wells, a small piece of black paper may be stuck behind the object, by simply wetting it with the tongue.[4]
[4] The side silver reflector is useful for illuminating such objects.