[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.
[3] I find, in Milne-Edwards’ ‘Leçons sur la Physiol. et l’Anat. comp.’ 3 page 197, the statement that, according to Frey and Leuckart, the heart of _Caprella linearis_ possesses _five_ pairs of fissures. I have examined perfectly transparent young Caprellæ (probably the young of Caprella attenuata, Dana, with which they occurred), but can only find the usual three pairs.
CHAPTER VII. STRUCTURE OF THE HEART IN THE EDRIOPHTHALMA.
Let us first glance over the extant facts.
Among the Stalk-eyed Crustacea (_Podophthalma_) we know only a very few species which quit the egg in the form of their parents, with the full number of well-jointed appendages to the body. This is the case according to Rathke[1] in the European fresh-water Crayfish, and according to Westwood in a West Indian Land Crab (_Gecarcinus_). Both exceptions therefore belong to the small number of Stalk-eyed Crustacea which live in fresh water or on the land, as indeed in many other cases fresh-water and terrestrial animals undergo no transformations, whilst their allies in the sea have a metamorphosis to undergo. I may refer to the Earthworms and Leeches among the Annelida, which chiefly belong to the land and to fresh water,—to the _Planariæ_ of the fresh waters and the _Tetrastemma_ of the sparingly saline Baltic among the Turbellaria,—to the Pulmonate Gasteropoda, and to the Branchiferous Gasteropoda of the fresh waters, the young of which (according to Troschel’s ‘Handb. der Zoologie’) have no ciliated buccal lobes, although such organs are possessed by the very similar Periwinkles (_Littorina_).