No attempt need now be made to discover the origin of parthenogenesis. Let it be assumed, for the moment, that it is a condition derived from hermaphroditism, wherein each individual is monœcious or bi-sexual. In all diœcious or uni-sexual animals, that is to say, where the individuals composing the species are either male or female, each contains a leaven of the opposite sex, even when adult. It is still a moot point whether, in the earlier stages of development, chance decides whether the sex shall be male or female, or, at any rate, whether the growing body is potentially male or female, till the die is cast by some as yet undiscovered factor; or whether this is determined from the very beginning of germinal life. In many of the lower animals, as among the Mollusca and some of the insects, each individual is as much male as female, and it is from a condition such as this that parthenogenesis probably had its rise.
These two groups are selected here because they, more than any others in like case, afford some extremely interesting gradations in this strange phenomena of what is to be regarded as the degeneration of sexual individuality, for each contains some members wherein the sexes are separate, and in these cases sexual desire is present in varying degrees. In some it is associated with very remarkable phenomena.
Among the Mollusca the Octopuses afford one of the most striking illustrations of such phenomena. In these creatures one of the sucker-bearing arms is more or less completely transformed to subserve the ends of sexual congress. Without entering into the technical details of the changes, it will suffice to remark that it is modified in such a way as to allow the transference of the spermatozoa from the body cavity wherein they are formed, to the arm near, or at, the tip of which they are stored in a special sac or “spermatophore,” and such modified arms are said to be “hectocotylized.” This extraordinary modification attains its maximum development in the celebrated Argonaut, and one or two of the more typical Octopuses. In the Argonaut this arm does not make its appearance until sexual maturity has been attained, when a large more or less globular swelling appears, enclosing the third arm of the left side, coiled upon itself. Having attained its full development the sac bursts and releases the arm. The folds which formed the sac now bend back to form a new receptacle into which the spermatophore is passed. But this is not all. The tip of the newly released arm bears another sac, which sooner or later bursts, forming a long, slender penis, and along the central tube of this the spermatozoa pass from the spermatophore to their destination. Their conveyance thereto forms the last and most amazing feature of this strange history. The male, eager with pent-up desire, and glowing with all the colours of the rainbow, gradually approaches the female of his choice, who apparently awaits him with no little palpitation, and then, with a sudden rush flings himself upon her, and apparently thrusts the penis into her mantle cavity, when at once the whole arm breaks off from his body and remains attached to her person, retaining its vitality, strange as it may seem, for some considerable time, during which, no doubt, the spermatozoa are slowly making their way out of the spermatophore and along the channel prepared for their reception. That the Cuttle-fish are polyandrous there seems to be little room for doubt, inasmuch as no less than four such detached arms have been found beneath the mantle of one female. With the majority of the Cuttle-fish and Octopus tribe the arm is not detached, but when it is so, and this occurs in all the species belonging to three different genera, a new arm is grown.
Plate 41.
SOME REMARKABLE METHODS OF “COURTSHIP.”
1. The female Argonaut and her egg-casket.
2 and 3. The male Argonaut and his “hectocotylized” arm.
4. A Cuttle-fish (Ocyhöe catenulata ♂), showing the “hectocotylized” arm described in the text, and the “spermatophore” at the base of the long filament.
[Face page 268.