122 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



ladder-like spicule may be detected in it by careful exam- 

 ination. The intestine is very much smaller than it was 

 at the preceding stage, and it now joins the anterior edge, 

 instead of the ventral surface of the globular stomach. 



g. The larva forty-eight hours older is shown in dorsal 

 view in Fig. 70. The arms {n) have lengthened slightly, 

 and their spicules (r) have formed a bridge across the dor- 

 sal surface of the body, close to the posterior end. The 

 posterior ends of the spicules [d) have almost disappeared. 

 The arms [q) have lengthened, and an elongated, ladder-like 

 spicule has appeared in each of them. The lateral angle 

 between the pre-oral and post-oral arms, now occupied 

 by the arm {n) is almost at the posterior end of the body. 

 This change of position is due in part to the excessive 

 growth of the organs anterior to the dotted line (x) in 

 part to the absorption of organs posterior to this line, and 

 in part to the movement of the angle {ii) of Figs. 67 and 

 68 towards the posterior end. 



Notice that a new spicule (m) makes its appearance on 

 the middle line of the dorsal surface over the oesophagus 

 at about this stage. 



b. The fully developed pluteus. 



This is shown in dorsal view in Fig. 71, and in ventral 

 view in Fig. 72. In Fig. 73, the spicular skeleton is 

 shown in its natural position, but without the soft parts. 



Notice that the dorsal and ventral lateral arms (71 and 

 72, q and n) are now fully developed, and are supported 

 by long spicules [r and t). The spicules (r) of the ventral, 

 lateral arms are simple, and their inner ends meet on the 

 median line to form a transverse bar {v) which carries at 

 each end, where it joins the brachial portion, a short 

 spine (w) , which runs forwards and outwards. 



The spicules {t) of the dorsal, lateral arms are ladder- 



