THE GROWTH OF JELLY-FISHES. |
A CHAPTER IN THE NEW ZOÖLOGY.
By Prof. W. K. BROOKS,
OF JOHNS HOPKINS UNIVERSITY.
II.
[Concluded.]
IN the first part of this article I described the life-histories of two hydroids: one, Liriope, in which each egg gives rise to only one jelly-fish, which is solitary and free at all stages of its existence, and without any power to multiply asexually; and a second species, Dysmorphosa, in which there is no limit to the number of adults to which a single egg may give rise, and in which the life-history is a complicated alternation of generations, with a sessile polymorphic hydroid stage from which the sexual jelly-fishes are produced by budding.
I shall now briefly sketch the more prominent features in the history of the process of specialization which has gradually evolved a complicated life-cycle like that of Dysmorphosa from one as simple and direct as that of Liriope, The parasitic jelly-fishes are peculiarly instructive in this connection. The genus Cunina includes a number of species which, while young, are parasites on other jelly-fishes. The free-swimming adult of one of them (Cunocantha octonaria) is shown in Fig. 9. It is quite
![](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/PSM_V33_D760_Jelly_fish_cunocantha_octonaria.jpg/400px-PSM_V33_D760_Jelly_fish_cunocantha_octonaria.jpg)
Fig. 9.—Side view of Cunocantha octonaria, slightly magnified, drawn from Nature by W. K. Brooks.
common upon the coast of Virginia and North and South Carolina. The adult is not a parasite, but as soon as the larvæ hatch from the eggs they make their way into the bell of another jelly-fish, and live there as parasites until they complete their development and assume the adult form. The jelly-fish which affords a home for these parasites is shown at k in Fig. 15. It is known as Turritopsis.