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distinguish these zooids from the ordinary organs of reproduction-detachment, and complexity of organisation.

The transition just noticed in the order of Polypifera is sufficient to show that differences in these points cannot be allowed any weight in a question of this kind. In regard particularly to what may be termed the adventitious organisation of the reproductive zooids, as compared with mere organs fulfilling the same function, this conclusion is strengthened by the contrast of a phenomenon of an opposite kind, -the degradation of individuals in certain species to the position of mere sexual mechanisms, these individuals being truly distinct from their origin-not mere zooids budded off from other forms, but animals developed independently from impregnated ova. The males of certain Rotifera, and still more those in the Cirripedia which are termed parasitic or complementary, are examples in point. In the structures now contrasted, we have examples of the two extremes of organisation; in the one case we have a member organised above par, so as to simulate a complete animal; in the other we have a true animal, so far below par in its structural development, as to resemble a mere organ. The contrast shows in a striking way that the suppression of normal parts in an animal, or the development of adventitious structures in connection with any particular organ, are not of essential importance in determining what has been termed by some authors "zoological individuality."

The other character-that of detachment-hinges on the proportionate development of the somatic life, that is, the life of the body as one whole, and the more or less independent life of its several organs or what we may term the topical or regional life. In the higher animals, the special actions of the several organs are as completely subordinated to that of the body as a whole, as are the powers of local corporations to the central government in any well-ordered state; yet there still remains sufficient evidence of the real existence of a distinct topical life. The antlers of the deer, and the hairs and teeth of animals generally, furnish well-marked illustrations of it. The first set of teeth, for instance, are formed, each in its own capsule, by a process of local growth, quite independent

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of that of the neighbouring tissues, nay, in so far opposed to it, that, at a certain stage of development, the integuments of the gum are partially disintegrated to allow of their eruption. A tooth thus generated by independent growth, sometime after attaining maturity, undergoes a process of decay ending in its ultimate removal, when a new tooth, of the second dentition, takes its place by a similar process of local development. In its turn this tooth also is shed, and though in most species it has no successor, yet in a few there is a constant succession during the whole lifetime of the animal. Such also is the case with the growth of the hair in all species. Hence in such local formations as teeth, hair, &c., we have, both in the way in which they are marked off from the neighbouring parts, and in this succession of growth, maturation, and decay-repeated again and again, and epitomizing, as it were, the life of the animal on which they grow-evidence of a vitality quite as defined perhaps in itself as that presented by the free zooids of the lower species, though the functional dependence on the common circulation and the mechanical bond of a common integument prevent their exhibiting the more obvious phenomena of a separate life. But as we descend in the scale of organisation, we come to species where, from the absence of centralising influences, the several organs-which are possessed of a vitality, less energetic perhaps, but more enduring than in the higher become emancipated, as it were, from the control of the general system, and appear as zooids, that is, in the guise of independent beings, rather than as integral parts of the same animal-suggesting the similitude of the feudal system of the middle ages, or of a loose confederation of Indian tribes, rather than of a well-ordered polity of our own day. And though the proper organs of reproduction, from their partial independence even in the higher animals, seem, as we might expect, to manifest most clearly this emancipation from the controlling influence of somatic life, yet it is seen very distinctly in others also, as, for instance, in the peculiarly modified tentacle of the Argonauta, which, when filled with spermatic fluid, is detached from the body, and finds its way spontaneously to the female, for the purpose of impregnation.

4. In the vegetable kingdom the correspondence of the archegonia formed in the prothallia or detached reproductive phytoids of ferns, to the intra-ovular structures of flowering plants, furnishes also an analogical argument of great weight in support of an essential community of nature between the proper organs of reproduction, and all such isolated gamomorphic forms, whether of the vegetable or the animal kingdom. This correspondence has been most satisfactorily traced by Hoffmeister and others, through the intermediate orders of Lycopodiaceæ, Marsileaceæ, and Coniferæ; but I need not make farther allusion to a subject on which I have nothing new. to bring forward, and which, in any case, could not be fairly treated in the limits of this paper.

It formed part of my original plan, to make a few observations on the relations of metamorphosis to alternation or metagenesis, and to follow up these general statements with some remarks on the principal modifications of the reproductive process in the leading groups of both kingdoms of nature, with the view of showing how far the protomorphic, orthomorphic, and gamomorphic stages are represented both in the alternating and non-alternating species; but the extent of my first draught of the subject has shown me how impracticable this would be within the limits of such an article as the present. In the meantime, therefore, I must content myself with such indications of these relations as are suggested by the annexed tabular views to which I have had occasion to direct attention in the course of this paper.*

* It is only since these remarks were sent to press that I have seen Radlkofer's observations on the function of reproduction in the animal and vegetable kingdoms. In the latter, this author distinguishes very clearly the varieties of alternation here termed Protomorphic and Gamomorphic, but in animals he seems only to recognise the first, so far, at least, as I can understand the translation of his paper in the "Annals of Natural History" (2d series, vol. xx., pp. 241, 344, 439).

TABLE I.

ALTERNATION OF GENERATIONS.

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of a Protomorphic Zooid,--e.g.

in Echinodermata of Auricularia, Bipinnaria, Pluteus; in Cestoidea-of Cystic Forms;

in Trematoda-of Infusorian, and Gregarinic Forms.

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as, in Echinodermata, of the Starfish or Sea Urchin; in Cestoidea, of the "Tania-head;"

in Trematoda, of the Cercariform Larva and the Distoma.

ORTHOMORPHIC STAGE.

Development of the Typical Form,

Pullulation in Polypifera and Polyzoa, of a series of Polypes cohering as a Polypidom; in Aphis, of successive swarms of free Larvæ, like the original.

of the Cellular Germ-Mass or "Mulberry Body."

Embryo-Buds," e.g.,

The "Gonophores and Blasto-styles" of the Polypifera;
The "Stolons" of the Tunicata.

of the "Primitive Trace" of Embryonic Organization.

As in Polypifera, of Medusiform Zooids in Salpa, of the Catenated Form; in Annelida, of Caudal Zooids;

in Cestoidea, of Proglottides.

Pullulation of Secondary Medusoids in Sarsia and some other Species.

Formation of " "Brood-Stocks," e. g.,

through the successive phases of Embryogeny; (Metamorphosis in the case of Larvæ or Naked Embryos, as in some Crustacea, Insects, and Batrachia.)

The Tissue of the immature Ovarian and Spermatic Glands.

GAMOMORPHIC STAGE.

Development of the proper Reproductive Structures,

as of Ovarian and Spermatic Follicles.

I

Formation of the Reproductive Elements, i.e., Ova and Cells with Spermatozoa. FECUNDATION OF THE OVUM.

ORDINARY REPRODUCTION.

CRYPTOGAMIA.

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Primary Development from the Fecundated Germ.

in Hepatice and Mosses, of the Theca, and Spores, which of the Cellular Pro-embryo or Suspensor. in the latter germinate into Protonemic Filaments

Pullulation of Derivative Protonemic Filaments;

1 Quaternate division of the Suspensor in Coniferæ. Formation of "Embryo-Buds," viz.:

the Gemma of the leafy axis of Mosses; 1 the Embryonic Cellular Mass.

ORTHOMORPHIC STAGE.

Development of the Typical Form or Vegetative Axis of the
Moss, Fern, or

I

Flowering Plant.

Pullulation of Successive Shoots, generally remaining in adhesion, but sometimes developed from deciduous bulbs.

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GAMOMORPHIC STAGE.

Development of the proper Reproductive Structures, viz.: in Ferns, of Prothallial Phytoids; I of Ovules and Pollen-grains.

Pullulation of occasional Secondary Prothallia in Ferns; I and of the "albuminous bodies" in Conifera.

Formation of the Reproductive Elements, viz.

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of Archegonia, with Germ-cells and Antheridia, with Cellules containing Antherozoids

The Floral Organs.

of Embryo-sacs with Germinal Bodies and Pollen-tubes with Fovilla

FECUNDATION.

(or in some Conifera, with Secondary Cellules).

PHANEROGAMIA.

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