NATURE 



\Junc i, 1882 



this article do not admit of our giving a summary of these 

 results, so we shall only allude to the one which is most 

 important. This is the discovery of the " Complemental 

 Males." The manner in which this discovery was made 

 in its entirety is of interest, as showing the importance of 

 remembering apparently insignificant observations which 

 may happen to be incidentally made during the progress 

 of a research. For Mr. Darwin writes : — 



•' When first dissecting Scalpellum vulgare, I was sur- 

 prised at the almost constant presence of one or more 

 very minute parasites, on the margins of both scuta, close 

 to the umbones. I carelessly dissected one or two speci- 

 mens, and concluded that they belonged to some new 

 class or order amongst the articulata, but did not at the 

 time even conjecture that they were cirripeds. Many 

 months afterwards, when I had seen in Ibla that an 

 hermaphrodite could have a complemental male, I remem- 

 bered that I had been surprised at the small size of the 

 vesiculae seminales in the hermaphrodite S. vulgar e, so 

 that I resolved to look with care at these parasites ; on 

 doing so I now discovered that they were Cirripedes, for 

 I found that they adhered bv cement, and were furnished 

 with prehensile antennas, which latter, I observed with 

 astonishment, agreed in every minute character, and in 

 size, with those of S. vulgare. I also found 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 pre- 

 sent more or less closely analogous phenomena. These 

 facts, together with those given under Ib)a (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 Scal- 

 pellum, as Males and Complemental Males " (vol. i. pp. 

 292-3). 



The remarkable phenomena of sexuality in these ani- 

 mals is summed up thus : — 



" The simple fact of the diversity in the sexual relations, 

 displayed within the limits of the genera Ibla and Scal- 

 pellum, 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) her- 

 maphrodites, with occasionally one, two, or three males, 

 capable of seizing and devouring their prey 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 pheno- 



mena here presented, I will allude to the marvellous 

 assemblage of beings seen by me within the sac of an 

 Itla quadrivahns, 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 larvae, with their curious 

 prehensile antennae, two great compound eyes, no mouth, 

 and six natatory legs ; and lastly, several hundreds of the 

 larva?, in their first stage of development, globular, with 

 horn-shaped projections on their carapaces, minute single 

 eyes, filiform antennae, 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 " Vari- 

 ation of Plants and Animals under Domestication," and 

 the " Descent of Man," we meet with many purely zoolo- 

 gical 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 particu- 

 larly allude to the chapters on Variability, Hybridism, 

 and Geographical Distribution — chapters which contain 

 such a large number of new facts, as well as new group- 

 ings of old ones, that we cannot undertake to epitomise 

 them in a resume 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 im- 

 portant part played in the economy of nature by 

 earthworms. Moreover, the hypothesis of sexual selec- 

 tion 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, con- 

 cerning the value of this collection 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 zoolo- 

 gical 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 suffi- 

 ciently 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 it was con- 

 sidered as propounding the only, the chief, or but a sub- 

 ordinate cause ; all that was needed to recommend the 

 evidence of evolution to the judgment of science was the 



