With respect to these organs, Mr. Mivart, as on so many previous occasions, asks: “What would be the utility of the first rudimentary beginnings of such structures, and how could such insipient buddings have ever preserved the life of a single Echinus?” He adds, “not even the sudden development of the snapping action would have been beneficial without the freely movable stalk, nor could the latter have been efficient without the snapping jaws, yet no minute, nearly indefinite variations could simultaneously evolve these complex coordinations of structure; to deny this seems to do no less than to affirm a startling paradox.” Paradoxical as this may appear to Mr. Mivart, tridactyle forcepses, immovably fixed at the base, but capable of a snapping action, certainly exist on some starfishes; and this is intelligible if they serve, at least in part, as a means of defence. Mr.

Agassiz, to whose great kindness I am indebted for much information on the subject, informs me that there are other starfishes, in which one of the three arms of the forceps is reduced to a support for the other two; and again, other genera in which the third arm is completely lost. In Echinoneus , the shell is described by M. Perrier as bearing two kinds of pedicellariae, one resembling those of Echinus , and the other those of Spatangus ; and such cases are always interesting as affording the means of apparently sudden transitions, through the abortion of one of the two states of an organ.

With respect to the steps by which these curious organs have been evolved, Mr. Agassiz infers from his own researches and those of Mr.