Page:Popular Science Monthly Volume 33.djvu/761

Rh The hydra which hatches from the egg of the Cunina is free, like the hydra-larva of Liriope. It has a short globular body, and an enormously elongated proboscis, at the tip of which the mouth is situated (Fig. 10). It has four short tentacles which are turned backward away from the mouth, and are terminated by round knobs, which are used for clinging to the body of the Turritopsis, for as the parasitic larva sucks its food out of the stomach of its host, it does not need to use its tentacles for capturing living animals. As soon as it finds its way into the bell of a Turritopsis it fastens itself securely by its tentacles to its inner surface in the angle at the base of the stomach, where it is in no danger of being swept away by the current which the Turritopsis produces while swimming, and, once securely fastened, it bends down its long proboscis, passes it up through the mouth of the Turritopsis into its stomach, and sucks out the digested food.

Turritopsis is shown at in Fig. 15; and Fig. 11, which I have copied from McCrady, the discoverer of this remarkable case of parasitism, shows the outline of the inner surface of the bell, and of the stomach of Turritopsis, with three of the parasitic Cunina larvæ in place, fastened by their tentacles, and with their mouths inserted into the stomach of their host.

Thus protected by the bell, and supplied with abundant food, which it neither captures nor digests, but sucks, all ready for assimilation, into its own stomach, the larva has a very "soft thing," and is naturally in no hurry to complete its development or to seek its fortune in the open water. It grows rapidly, acquires more tentacles, and, as its stomach grows larger, and it becomes able to suck in and to assimilate more food than it needs