298 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII. 



and Alexander Agassiz has seen an Echinus or sea-urchin 

 rapidly passing particles of excrement 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 de- 

 fence. 



"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 struc- 

 tures, and how could such incipient buddings have ever 

 preserved the life of a single Echinus? " He adds, " not 

 even the sudden development of the snapping action 

 could have been beneficial without the freely moveable 

 stalk, nor could the latter have been efficient without 

 the snapping jaws, yet no minute merely indefinite 

 variations could simultaneously evolve these complex 

 co-ordinations 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 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, informs 

 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 pedi- 

 cellarias, one resembling those of Echinus, and the other 

 those of Spatangus; and such cases are always inter- 

 esting as affording the means of apparently sudden 



