194 THE ORIGIN OF SPECIES 



on the assumption that they are descended from a marsupial 

 form), "this at least perfectly innocent and harmless structure?" 

 It may be suggested in answer, that the voice, which is certainly 

 of high importance to many animals, could hardly have been used 

 with full force as long as the larynx entered the nasal passage; 

 and Professor Flower has suggested to me that this structure would 

 have greatly interfered with an animal swallowing solid food. 



We will now turn for a short space to the lower divisions of 

 the animal kingdom. The Echinodermata (star-fishes, sea-urchins, 

 etc.) are furnished with remarkable organs called pedicellariae, 

 which consist, when well developed, of a tridactyle forceps — that 

 is, of one formed of three serrated arms, neatly fitting together and 

 placed on the summit of a flexible stem, moved by muscles. These 

 forceps can seize firmly hold of any object; and Alexander Agassiz 

 has seen an Echinus or sea-urchin rapidly passing particles of ex- 

 crement from forceps to forceps down certain lines of its body, in 

 order that its shell should not be fouled. But there is no doubt that 

 besides removing dirt of all kinds, they subserve other functions; 

 and one of these apparently is defence. 



With respect to these organs, Mr. Mivart, as on so many pre- 

 vious occasions, asks: "What would be the utility of the first rudi- 

 mentary beginnings of such structures, and how could such incip- 

 ient buddings have ever preserved the life of a single Echinus?" 

 He adds, "Not even the sudden development of the snapping ac- 

 tion could have been beneficial without the freely movable stalk, 

 nor could the latter have been efficient without the snapping jaws, 

 yet no minute, merely 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, immov- 

 ably fixed at the base, but capable of a snapping action, certainly 

 exist on some star-fishes; 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, in- 

 forms me that there are other star-fishes, 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 



