342 



COMPARATIVE ANATOMY 



CHAP. 



moving from left to right may be marked a, the second h, and these letters may- 

 further indicate the rows to which these plates belong. In this way we can 

 name each of the ten ambulacral plates bordering the peristome. Examining 

 these ten plates carefully, we see that those indicated by la, lla, IIU, R'a, \h 



-=="=31 



Fig. 302. — Kleinia luzonica (Gray). Apical system, spread ont (after Lov^n). /a, Fascicles. 

 Further e.xplanations in the adjoining text. 



are larger and possess two pores each, while the smaller plates 16, 116, Ilia, IV6 

 and \n 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 II 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 hut for their young stages also) ; the plates la, Ila, III6, I\^a, \h are 



