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Show 192 DIFFICULTIES ON THEORY. CHAP. VI. called by me the ovigerous frena, whic!l serve, throug~1 the means of a sticky secretion, to retam the e~g~ until they are hatched within the sack. These e1rr1pedes have no branchire, the whole surface of the body and sack, including the small frena, serving for respiration. The Balanidre or sessile cirripedes, on the other hand, have no ovigerous frena, the eggs lying loose at the bottom of the sack, in the well-enclosed shell ; but they have large folded branchire. NoV: I think no o~e will dispute that the ovigerous frena 111 the one family are strictly homologous with the branchire of the other family; indeed, they graduate into each other. Therefore I do not doubt that little folds of skin, which originally served as ovigerous frena, but which, likewise, very slightly aided the act of respiration, have been gradually converted by natural selection into branchim, simply through an increase in their size and the obliteration of their adhesive glands. If all pedunculated cirripedes had become extinct, and they have already suffered far more extinction than have sessile cirripedes, who would ever have imagined that the branchim in tllis latter family had originally existed as organs for preventing the ova from being washed out of the sack? Although we must be extremely cautious in concluding that any organ could not possibly have been produced by successive transitional gradations, yet, undoubtedly, grave cases of difficulty occur, some of which will be discussed in my future work. One of the gravest is that of neuter insects, which are often very differently constructed from either the males or fertile females; but this case will be treated of in the next chapter. The electric organs of fishes offer another case of special difficulty; it is impossible to conceive by what steps these wondrous organs have been produced ; but, as Owen and others have ren1arked, CHAP. VI. TRANSITIONS OF ORGANS th . . . . 193 eir Intimate structure closel muscle ; and as it has I t I ~ resembles that of common an organ closely analog~u~ ro :~: sihow~ that Rays have y~t do not, as Matteuchi asserts ed~:tnc apparatus, and City, we must own that we ./!: ' c~arge any electri-th t are 1ar too Ign t a no transition of any k. d . . oran to argue Th . In Is possible . e e.Iectnc organs offer another . senous difficulty . for th . and even more fi h ' ey occur In onl b s es, of which several ar . d 1 y a out a dozen affinities. Generally when t~ WI e y remote in their several members of th e same organ appears in b e same class es . 11 . . mem ers having very d . .c£' • ' peCia Y if In t .b Iuerent habits f I . .{.' a tri ute its presence t . h . o lle, we may 0 In entance f ancestor ; and its absence . rom a common its loss through disuse or I~ so:ue of ~he members to electric organs had bee n~ hura. selection. But if the . n In erited fr . progenitor thus provided . om one ancient all electric fishes would' :a: ~ght have. expected that each other. Nor does I e een speCially related to that formerly most fis~:so ~g~ at all ~ead to the belief most of their modified d a delectric organs, which presence of luminous esc~n ants have lost. The · organs In a fe · Ing to different families d w Insects, belong-case of difficulty Oth an orders, offers a parallel stance in plants . the v er cas~s could be given ; for inof pollen-grain~ bo ery CUriOUS contrivance of a mass gland at the end I·s trnh e on a. foot-stalk ·with a sticky genera almost as' remeo ts ame m 0. rch I·s an d Asclepias,- plants. In all th e as possible amongst flowering C·i es furnished •the se cases of t wo very d.I sti. nct spe-organ, it should: b appa~ently the same anomalous appearance and fun~t::~v:f that, although the general yet some fundamental diffi the organ may be the same, tected. I am inclined to b ~renee ca~ generally be deway as two men hav e e~e tha.t In nearly the same e sometimes Independently hit on K |