342 



COMPARATIVE ANATOMY 



CHAP. 



these ten plates carefully, we see that those indicated by la, lla, I 



FIG. 302. Kleinia luzonica (Gray). Apical system, spread out (after Loven). fa, Fascicles. 

 Further explanations in the adjoining text. 



are larger and possess two pores each, while the smaller plates Ib, lib, Ilia, I\ b 

 and Va have only one pore each. Only the ambulacra I and V, i.e. the two 

 posterior ambulacra, are thus bilaterally symmetrical, while the two (paired) 

 anterior ambulacra 17 and IV, and the two rows of plates of the anterior unpaired 

 ambulacrum III, are asymmetrical. This law holds for all Echinoidea (not only 

 for adults but for their young stages also) ; the plates la, Ha, lllb, IVa, V6 are 



