Let us turn then to a wider field, that of the developmental history of the Crustacea, upon which science has already brought together a varied abundance of remarkable facts, which, however, have remained a barren accumulation of unmanageable raw-material, and let us see how, under Darwin’s hand, these scattered stones unite to form a well-jointed structure, in which everything, bearing and being borne, finds its significant place. Under Darwin’s hand! for I shall have nothing to do except just to place the building stones in the position which his theory indicates for them. “When kings build, the carters have to work.” [1] The young animals in the egg, a little before their exclusion, are usually particularly convenient for the observation of the fissures in the heart; they are generally sufficiently transparent, the movements of the heart are less violent than at a later period, and they lie still even without the pressure of a glass cover. Considering the common opinion as to the distribution of the Amphipoda, namely, that they increase in multiplicity towards the poles, and diminish towards the equator, it may seem strange that I speak of a considerable number of species on a subtropical coast. I therefore remark that in a few months and without examining any depths inaccessible from the shore, I obtained 38 different species, of which 34 are new, which, with the previously known species (principally described by Dana) gives 60 Brazilian Amphipoda, whilst Kröyer in his ‘Grönlands Amfipoder’ was acquainted with only 28 species, including 2 Læmodipoda, from the Arctic Seas, although these had been investigated by a far greater number of Naturalists. [2] According to Milne-Edwards’ arrangement the females of this genus would belong to the “Hypérines ordinaires” and the previously unknown males to the “Hypérines anormales,” the distinguishing character of which, namely the curiously zigzagged inferior antennæ, is only a sexual peculiarity of the male animals. In systematising from single dead specimens, as to the sex, age, etc. of which nothing is known, similar errors are unavoidable. Thus, in order to give another example of very recent date, a celebrated Ichthyologist, Bleeker, has lately distinguished two groups of the Cyprinodontes as follows: some, the Cyprinodontini, have a “pinna analis non elongata,” and the others, the Aplocheilini, a “pinna analis elongata”: according to this the female of a little fish which is very abundant here would belong to the first, and the male to the second group. Such mistakes, as already stated, are unavoidable by the “dry-skin” philosopher, and therefore excusable; but they nevertheless prove in how random a fashion the present systematic zoology frequently goes on, without principles or sure foundations, and how much it is in want of the infallible touchstone for the value of the different characters, which Darwin’s theory promises to furnish.