THE DEVELOPMENT OP ASTBEINA GIBBOSA. 287 



Fig. 61.— Section of larva about Stage F, to show the mutual relations of 

 the stone-canal, the axial sinus (»'.), the right dorsal horn of the left poste- 

 rior coelom {l"p"c".), and the right hydrecoele [rhi/.). 



Figs. 62— 69.— Eight sections of a larva slightly older than Stage F, to 

 show the relation of the arm rudiments to the lobes of the hydroooele. Fig. 63 

 shows the incipient healing of the breach in the septum between the anterior 

 ccelom (axial sinus) and the left posterior coelom. Figs. 64 and 65 show that 

 arm rudiment No-. V is still widely separated from hydrocoele lobe 1 by the 

 base of the stalk, and also that the right ventral horn {I'p'd.) of the left 

 posterior coelomis not completely separated from the axial sinus (a'.). Fig. 65 

 also shows the complete separation of the hydrocoele from the axial sinus. 

 Figs. 66 and 67 show relation of the oral coelom {or. c.) to the adult oesopha- 

 gus {a. OS.). Fig. 69 shows the adhesive disc of the stalk {^x.) attached to a 

 piece of Alga (x), and the rest of the ectoderm of the prseoral lobe being 

 invaginated {hist) to undergo destruction. It also shows that each primary 

 lobe of the hydrocoele has developed two pairs of secondary lobes. 



PLATE XV. 



The same remarks apply to Figs. 70 — 78 as to the contents of the three 

 foregoing plates. Figs. 79 — 82 are sections cut parallel to the disc of the 

 star-fish or "adult plane," the magnification being the same, viz. 80 dia- 

 meters. 



Figs. 70 and 71. — Two sections of a larva of Stage G. Fig. 70 shows the 

 relationship which the adiilt and the larval oesophagus occupy with regard to 

 one another, the latter being a mere rudiment unconnected with the gut ; it 

 also shows the outgrowths from the adult oesophagus. Fig. 71 shows the 

 oral coelom opening into left posterior coelom ventrally by breaking down of the 

 partition between them ; also the first trace of the pyloric cseca as outgrowths 

 from the pyloric sac. 



Fig. 72. — Section of larva rather older than Stage G. The adult i^iouth is 

 formed, and the oral coelom opens widely into the left posterior ccelom. The 

 stalk has become a small solid rudiment. The dotted line shows the boundary 

 between the pyloric sac and the adult " oesophagus " or "stomach." 



Fig. 73. — Section of a larva of the same age as the preceding ; it shows the 

 two dorsal pyloric caeca already formed, also the so-called heart or " ovoid 

 gland " (ovff.), as a fold projecting into the axial sinus («'.). 



Pjq_ 74. — Another section from the same series as Fig. 72. Shows the two 

 ventral pyloric cseca ; it is seen also that their suspensory mesenteries are 

 derived from the mesentery separating the right posterior coelom from the left 

 (compare Fig. 75). Note also that the tube-feet have acquired their suckers. 

 The animal has broken loose from its attachment, which accounts for the 

 rudimentary condition of the stalk. 



