varying from 12 to 72 hours; and upon post-mortem examination of the body, no less than ten young tænia were found in the intestine, four of which could be distinctly recognized as specimens of Tænia solium.

Finally, both Leuckart and Küchenmeister' have shown, on the other hand, that the eggs of Taenia solium, introduced into the body of the pig, will give rise to the development of Cysticercus cellulosa: thus demonstrating that the two kinds of parasites are identical in their nature, and differ only in the manner and degree of their development.

There remains, accordingly, no good reason for believing that even the encysted parasites are produced by spontaneous generation. Whatever obscurity may hang round the origin or reproduction of any class or species of animals, the direct investigations of the physiologist always tend to show that they do not, in reality, form any exception to the general law in this respect; and the only opinion which is admissible, from the facts at present within our knowledge, is that organized beings, animal and vegetable, wherever they may be found, are always the progeny of previously existing parents.

Op cit., p. 120.

CHAPTER II.

ON SEXUAL GENERATION, AND THE MODE OF ITS

Fig. 157.

ACCOMPLISHMENT.

d

THE function of generation is performed by means of two sets of organs, each of which gives origin to a peculiar product, capable of uniting with the other so as to produce a new individual. These two sets of organs, belonging to the two different sexes, are called the male and female organs of generation. The female organs produce a globular body called the germ, or egg, which is capable of being developed into the body of the young animal or plant; the male organs produce a substance which is necessary to fecundate the germ, and enable it to go through with its natural growth and development.

a

BLOSSOM OF CONVOLVULUS PURPUREUS. (Morning glory.)-a. Germ. b. Pistil. c. c. Stamens, with authers. d. Corolla e. Calyx

Such are the only essential and universal characters of the organs of generation. These organs, however, exhibit various additions and modifications in different classes of organized beings, while they show throughout the same fundamental and essential characters.

In the flowering plants, for example, the blossom, which is the generative apparatus (Fig. 157), consists first of a female organ containing the germ (a), situated usually upon the highest part of the leaf-bearing stalk. This is surmounted by a nearly straight column, termed the pistil (b), dilated at its summit into a globular expansion, and occupying the centre of the flower. Around it are arranged several slender filaments, or stamens, bearing upon their extremities the male organs, or anthers (c, c). The

whole is surrounded by a circle or crown of delicate and brilliantly colored leaves, termed the corolla (d), which is frequently provided with a smaller sheath of green leaves outside, called the calyx (e). The anthers, when arrived at maturity, discharge a fine organic dust, called the pollen, the granules of which are caught upon the extremity of the pistil, and then penetrate downward through its tissues, until they reach its lower extremity and come in contact with the germ. The germ thus fecundated, the process of genera tion is accomplished. The pistil, anthers, and corolla wither and fall off, while the germ increases rapidly in size, and changes in form and texture, until it ripens into the mature fruit or seed. It is then ready to be separated from the parent stem; and, if placed in the proper soil, will germinate and at last produce a new plant similar to the old.

Fig. 158.

In the above instance, the male and female organs are both situated upon the same flower; as in the lily, the violet, the convolvulus, &c. In other cases, there are separate male and female flowers upon the same plant, of which the male flowers produce only the pollen, the female, the germ and fruit. In others still, the male and female flowers are situated upon different plants, which otherwise resemble each other, as in the willow, poplar, and hemp.

In animals, the female organs of generation are called ovaries, since it is in them that the egg,

or "ovum," is produced. The
male organs
are the testicles,
which give origin to the fecun-
dating product, or "seminal
fluid," by which the egg is fer-
tilized. We have already men-
tioned above that in the articula-
tions of the tapeworm the ovaries
and testicles are developed to-
gether. (Fig. 158.) The ovary

SINGLE

a

a, a, a. Ovary filled with eggs. b. Testicle. c. Genital orifice.

(a, a, a) is a series of branching follicles terminating in rounded extremities, and communicating with each other by a central canal. The testicle (b) is a narrow, convoluted tube, very much folded

upon itself, which opens by an external orifice (c) upon the lateral border of the articulation, about midway between its two extremities. The spermatic fluid produced in the testicle is introduced into the female generative passage, which opens at the same spot, and, penetrating deeply into the interior, comes in contact with the eggs, which are thereby fecundated and rendered fertile. The fertile eggs are afterward set free by the rupture or decay of the articulation, and a vast number of young produced by their development.

In snails, also, and in some other of the lower animals, the ovaries and testicles are both present in the same individual; so that these animals are sometimes said to be "hermaphrodite," or of double sex. In reality, however, it appears that the male and female organs do not come to maturity at the same time; but the ovaries are first developed and perform their function, after which the testicles come into activity in their turn. The same individual, therefore, is not both male and female at any one time; but is first female and afterward male, exercising the two generative functions at different ages.

In all the higher animals, however, the two sets of generative organs are located in separate individuals; and the species is consequently divided into two sexes, male and female. All that is absolutely requisite to constitute the two sexes is the existence of testicles in the one, and of ovaries in the other. Beside these, however, there are, in most instances, certain secondary or accessory organs of generation, which assist more or less in the accomplishment of the process, and which occasion a greater difference in the anatomy of the two sexes. Such are the uterus and maminary glands of the female, the vesiculæ seminales and prostate of the male. The female naturally having the immediate care of the young after birth, and the male being occupied in providing food and protection for both, there are also corresponding differences in the general structure of the body, which affect the whole external appearance of the two sexes, and which even show them. selves in their mental and moral, as well as in their physical characteristics. In some cases this difference is so excessive that the male and female would never be recognized as belonging to the same species, unless they were seen in company with each other. Not to mention some extreme instances of this among insects and other invertebrate animals, it will be sufficient to refer to the well known examples of the cock and the hen, the lion and lioness, the

buck and the doe. In the human species, also, the distinction between the sexes shows itself in the mental constitution, the disposition, habits, and pursuits, as well as in the general conformation of the body, and the peculiarities of external appearance.

We shall now study more fully the character of the male and female organs of generation, together with their products, and the manner in which these are discharged from the body, and brought into relation with each other.