life, and a small bell (e), which, however, grows very rapidly, so that the animal soon assumes the adult form, shown in Fig. 9. The life-history of this species of Cunina is given in the following diagram:

III. CUNINA OCTONARIA.-Egg = Planula =

The egg becomes converted into a planula, this into a hydra, and this into a medusa, exactly as in the case of Liriope, except that the case is complicated by the budding of new hydras, each of them destined to become a medusa, from the body of the hydra which hatches from the egg, during its parasitic life, and before it becomes a medusa. Each Liriope-egg produces only one adult, while the number of adults which may be derived from a Cunina egg is quite large, although every individual in the series ultimately becomes an adult, and multiplies by sexual reproduction.

In another species of Cunina, Cunocantha parasitica, a new complication is introduced, for the hydra which hatches from the egg never becomes a jelly-fish, but remains a parasite as long as it lives, budding off other larvæ which grow up into adults. life-history is like this:

Its

(Hydra = Medusa < eggs.

IV. CUNOCANTHA PARASITICA.-Egg = Planula = Hydra x Hydra Medusa < eggs. Hydra Medusa < eggs.

If the hydras which are formed by budding were to remain as hydras, like the one which hatches from the egg, and were to bud off jelly-fish, we should have a life-history which is exhibited by many species, and is shown in this diagram:

Turritopsis, the jelly-fish, which is infested by the Cunina larvæ, has a life-history which is very similar to the one given in this diagram, with the addition of a slight but highly important modification.

The planula is shown in the left-hand lower corner of Fig. 2. It soon attaches itself to some solid body and becomes a root, which goes no further, but, as shown in the right-hand lower corner of Fig. 2, soon produces a bud which becomes a feeding hydra. Multiplication by budding now goes on rapidly, in such a way as to

build up a branching, tree-like colony, with a feeding hydra at the tip of each twig. Two branches from one of these trees are shown in Fig. 15. Ultimately each of these hydras produces a number

T

of buds around the base of its body, as shown at B in the figure, and these buds ultimately become detached and grow up into the adult jelly-fish, K.

The life-history of Turritopsis is therefore like this, and the chain which connects the egg with the adult is broken three times, for the root, which is directly derived from the egg, goes no further, nor do the hydras which bud from the root become jellyfish, and the latter form still a third set of individuals.

The larval life is long and important; the number of sexual adults produced by each egg is very great indeed, and the life-history is extremely complicated, but each one of the individuals is in the direct line of succession; for, while neither the root nor the hydras ever become converted into any higher form, the root produces hydras, and each one of these produces jelly-fish.

In the next species to be considered, a Eutima which is common on our coast (Fig. 16), another stage of complexity is introduced by the restriction of the power to bud jelly-fish to certain hydras, while others become specialized for nutrition. This specialization has come about gradually, and the various species of living hydroids exhibit all the steps in the process. In some species, as in Turritopsis, all the hydras perform both functions, and are alike in structure; in others, those which are placed at the tips of the branches and are best able to obtain food devote themselves to this purpose and produce no jellyfish, while these are budded only from those hydras which are near the base of the colony. In some cases the two sets of hydras are alike in structure, but in other species the feeding hydras at the tips of the branches are very large, with capacious stomachs and long tentacles, while the reproductive hydras have small tentacles and mouths. In still

FIG. 17.

other species, as in Eutima, they are true blastostyles, without mouths, and with rudimentary tentacles, and all the work of nutrition is performed by the feeding hydras.

After a short swim

The planula of Eutima is shown in Fig. 17. ming life, it fastens itself to some solid body, and elongating, be

comes a root (Fig. 18); and a bud, m, soon grows out from it to form the first feeding hydra, which soon acquires a mouth (Fig. 19, 1) and tentacles, i, and begins to capture and digest food and to accumulate a reserve of nutriment, while the root continues to throw

out new buds, as shown in Fig. 18 at m. For a long time all the buds become feeding hydras; but at last, when the mouths are numerous enough, buds which remain mouthless are formed, and become the blastostyles or jelly-fish producers. The following diagram shows the life-history of Eutima:

Diagram No. 1, which was given in the beginning of this article, to illustrate the life of Dysmorphosa, shows the next stage in the process of complication, and a comparison will show that it is derivable from Diagram VI by slight changes, just as VI is derivable from V, and this from the preceding, and so on until finally we reach a simple, direct life-history, in which each egg produces one adult, which passes through a transitory larval hydra stage.

Forty years ago, a zoologist of the old school might have believed that the life-history of Dysmorphosa has always been complex, and that of Liriope always simple; but the doctrine that all the representatives of any great group of animals owe their common characteristics to descent from a common ancestor is one of the fundamental principles of modern elementary zoology, and as this doctrine forms the basis rather than the aim of this article, I assume, without discussion, that the remote ancestors of Liriope