494 



INVERTEBEATA 



CHAP. 



growth of the left hydrocoele is accompanied by a growth of the 

 whole left side of the larva. Thus we find that by this growth the 

 left antero-lateral larval arm is carried across to the right side, so as 

 to lie close to its right partner, whilst the left postero-dorsal arm is 

 carried forwards to a position where it might easily be mistaken for 

 the left antero-lateral arm (Fig. 377, C). 



The left anterior coelom and its pore - canal are also earned 

 forwards till they reach the mid-dorsal line, in other words, till they 

 reach a position similar to that which they reach in the Asteroid 



FiG. 378.- 



-Loiigitudiiial frontal section of a larva of Ophiothriz frt 

 stage of metamorphosis. (Original.) 



in the first 



3, 4, 5, third, fourth, and fifth primary lobe of the hydrocoele respectively, ep./, epineural fold ; 

 int, intestine ; l.p.c, left posterior coelom ; UpU^, right ventral horn of the left posterior coelom ; p.h.SA, 

 p.hA.5, perihaemal rudiments intervening between lobes 3 and 4, and lobes 4 and 5, respectively, of the 

 hydrocoele ; p.vac, posterior vacuolated crest ; s(, stomach ; stoin, stomodaeum. 



larva at the same stage. The left posterior coelom sends out a right 

 ventral horn (l^p'^c^, Fig. 378) which sweeps over to the right side, 

 beneath the oesophagus, and eventually meets the horn of the same 

 cavity which has extended dorsal to the oesophagus, thus forming a 

 complete ring. Two of the arm rudiments are formed from this 

 horn, the other three arise from the main part of the left posterior 

 coelom. 



From the inner side of the left posterior coelom there are given 

 off wedge-shaped, thick-walled evaginations, which alternate with 

 the lobes of the hydrocoele and extend ventrally to them. These are 

 the rudiments of the perihaemal ring'-canal, and of the radial 



