306 



P. HERBERT CARPENTER. 



position of the eye-spot.''' One or two further arguments may 

 be adduced in favour of this view. 



1. The embryonic radials of Ophiurids always remain upon 

 the abactinal surface of the adult in the neighbourhood of the 

 dorsocentral, and in many species develope into large plates, 

 the primaries, which form a closed ring around the dorsocentral, 

 just as in the early stages of the young Amphiura (fig. i, 4), 

 though they are sometimes separated from it by intermediate 



Fig. I. — (' Quart. Journ. Micr. Sci.,' 1882, vol. xxii, p. 379.) Apical system 

 of the young Amphiura squamata ; Stage I, after Ludwig. 1. Dorso- 

 central. 4. Radials. 5. Orals. T. Terminals. ad v Second adambula- 

 cral plates, w. p. Water-pore. 



plates (fig. ii, 2, 3). The oculars of an Urchin are also confined 

 to the abactinal surface, and are separated from the dorso- 

 central by one ring of plates ; while in most Crinoids the 

 radials form a closed ring as in the earliest Amphiura, 

 sometimes with one and sometimes with two rings of plates 

 within them, just as in the two subsequent stages of the deve- 

 lopment of Amphiura. 



