THE DEVELOPMENT OP ASTBEINA GIBBOSA. 245 



future star-fish are decidedly oblique to one another, being 

 closely apposed posteriorly, but anteriorly separated by the 

 thick base of the stalk. We see also that a lateral shift of the 

 arm rudiments has commenced, No. V having passed beyond 

 the hydrocoele lobe No. 5, and so also in the case of the others. 

 A second pair of rudiments of tube-feet has grown out from 

 each lobe of the hydrocoele, so that they are now 5-partite. 



Figs.62— 69,Pl.XIV,are taken from a most instructive series 

 of sections of a larva of this age, and are intended to give a 

 clear conception of its internal anatomy. We are struck at 

 once by the great reduction of the stalk, although ventrally 

 (fig. 66) the stalk coslom still communicates with the axial 

 sinus. In fig. 65 we see the last trace of the secondary ventral 

 communication between the left posterior coelom {I'p'c') and 

 the axial sinus a' (anterior ccelom) just closing. The secondary 

 dorsal opening persists much longer, but fig. 63 shows us that 

 it also is beginning to be closed. Comparing figs. 64 and 65, 

 we see that the adult oesophagus has acquired two lateral out- 

 growths, one directed anteriorly, the other posteriorly ; there is 

 also a third horn directed dorsally, which of course cannot be 

 seen in the sections. Fig. 67 shows how the oral coelom {orx) 

 now half encircles the adult oesophagus. As to the arm rudi- 

 ments, the most interesting thing is to notice the wide separa- 

 tion of No. V from the hydrocoele lobe No. 1. When the 

 intervening tissue shrinks, a change which involves a reduction 

 in size of the axial sinus (compare a'., PI. XV, figs. 75 and 76), 

 the metamorphosis will be complete. The incipient shift of the 

 other rudiments is seen, especially in the case of Nos. II and 

 III, the latter falling between lobes 3 and 4. 



By a continuation of the processes referred to above, viz. 

 the constriction of the base of the stalk, the increasing 

 flexure of the body on it, and the continued growth of the 

 hydrocoele and left posterior coelom, we soon reach Stage G, 

 which is represented in PI. XI, figs. 17 and 18. We notice the 

 great reduction of the stalk (which is now usually directed 

 downwards almost at right angles to the disc, though the 

 extent of the angle between the two varies) and the completion 



