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with prehensile antennæ, which latter, I observed with astonishment, agreed in every minute character, and in size, with those of S. vulgare. I also found
I that these parasites were destitute of a mouth and stomach; that consequently they were short-lived but that they reached maturity; and that all were males. Subsequently five other species of the genus Scalpellum were found to present more or less closely analogous phenomena. These facts, together with those given under Ibla (and had it not been for this latter genus, I never probably should have struck on the right line in my investigation), appear sufficient to justify me in provisionally considering the truly wonderful parasites of the several species of Scalpellum, as Males and Complemental Males' (vol. i. pp. 292-3).
. The remarkable phenomena of sexuality in these animals is summed up thus :
“The simple fact of the diversity in the sexual relations displayed within the limits of the genera Ibla and Scalpellum, appears to me eminently curious. We have (1) a female, with a male (or rarely two) permanently attached to her, protected by her, and nourished by any minute animals which
may enter her sac; (2) a female, with successive pairs of short-lived males, destitute of mouth and stomach, inhabiting the pouches formed on the under sides of her two valves; (3) an hermaphrodite, with from one or two, up to five or six, similar short-lived males without mouth or stomach, attached to one particular spot on each side of the orifice of the capitulum ; and (4) hermaphrodites, with occasionally one, two, or three males, capable of seizing and devouring their prey in the ordinary
in the ordinary Cirripedal method, attached to two parts of the capitulum, in both cases being protected by the closing of the scuta.”
With reference to these Complemental Males (so called " to show that they do not pair with a female, but with a bisexual individual”) Mr. Darwin further observes: “Nothing strictly analogous is known in the animal kingdom; but amongst plants, in the Linnean class Polygamia, closely similar instances abound;” and also that“ in the series of facts now given we have one curious illustration more to the many already known, how gradually nature changes from one condition to the other, in this case from bisexuality to unisexuality” (ii. 29).
Lastly, to give only one other quotation from this work, he writes :
“As I am summing up the singularity of the phenomena here presented, I will allude to the marvellous assemblage of beings seen by me within the sac of an Ibla quadrivalvis, namely, an old and young male, both minute, worm-like, destitute of a capitulum, with a great mouth and rudimentary thorax and limbs, attached to each other and to the hermaphrodite, which latter is utterly different in appearance and structure; secondly, the four or five free, boat-shaped larvæ, with their curious prehensile antennæ, two great compound eyes, no mouth, and six natatory legs; and lastly, several hundreds of the larvæ, in their first stage of development, globular, with horn-shaped projections on their carapaces, minute single eyes, filiform antennæ, probosciform mouths, and only three pairs of natatory legs. What diverse beings, with scarcely anything in common, and yet all belonging to the same species !” (i. 293).
Scattered through the Origin of Species, the Variation of Plants and Animals under Domestication, and the Descent of Man,' we meet with many purely
zoological observations of much interest and importance as such, or apart from their bearing on the general principles and arguments for the illustration or fortification of which they are introduced. In this connection we may particularly allude to the chapters on Variability, Hybridism, and Geographical Distribution-chapters which contain such a large number of new facts, as well as groupings of old ones, that we cannot undertake to epitomise them in a résumé of Mr. Darwin's work so brief as the present. Nor should we forget to mention in the present connection his experimental proof of the manner in which bees make their hexagonal cells, and of the important part played in the economy of nature by earthworms. Moreover, the hypothesis of sexual selection necessitated the collection of a large body of facts relating to the ornamentation of all classes of animals, from insects and crustacea upwards; and whatever we may think about the stability of the hypothesis, there can be no question, from a zoological point of view, concerning the value of this collection of facts as such.
But without waiting to consider further the purely
zoological results presented by the work before us, we must turn to consider the effects of this work upon zoological science itself.
And here we approach the true magnitude of Darwin as a zoologist. Of
very few men in the history of our race can it be said that they not only enlarged science, but changed it—not only added facts to the growing structure of natural knowledge, but profoundly modified the basal conceptions upon which the whole structure rested ; and of no one can this be said with more truth than it can be said of Darwin. For although it is the case that the idea of evolution had occurred to other minds-in two or three instances with all the force of full conviction—it is no less certainly the case that the idea proved barren. Why did it prove so ? Because it had never before been fertilised by the idea of natural selection. To demonstrate, or to render sufficiently probable by inference, the fact of evolution (for direct observation of the process is from the nature of the case impossible), required some reasonable suggestion as to the cause of evolution, such as is supplied by the theory of natural selection; and when once this suggestion was forthcoming, it mattered little whether