444 



Prof. E. W. MacBride. Some Points in the [May 6. 



five finger-like prolongations (fig. 4), thus proclaiming itself to be the rudiment 

 of the hydroccele, or water- vascular system of the adult. Sections demonstrate 

 that its persisting connection with the anterior ccelom which constitutes the 

 stone-canal, as in the case of Asterina gibbosa, is situated between lobes 1 

 and 2. 



Fig. 2. 



Fig. 3. 



Fig. 4. 



lf.cS \J^-~S's' ' -r.p.c. Lp.c.'-'" \^>- — y y r.p.c. tfA 



Fig. 2.— Diagram of larva, showing coelom divided on left side and dividing on right side. 

 Fig. 3. — Diagram of larva, showing formation of rudiments of hydroceles from the 



posterior ends of the anterior coelomic sacs. 

 Fig. 4. — Diagram of larva, showing first stages of metamorphosis. Notice migration of 



pore towards the right. l.a.c. y left anterior ccelom ; l.p.c, left posterior 



coelom ; l.hy., left hydroccele ; I'.p'.c'., right horn of left posterior ccelom ; 



r.a.c, right anterior coelom ; r.hy^ right hydroccele ; r.p.c, right posterior 



ccelom ; p.c, pore-canal. 



The metamorphosis of the larva into the adult form now commences, This 

 is initiated by a preponderant growth of the leftside. The hydroccele enlarges, 

 its lobes grow longer, and its anterior end commences to extend dorsally to the 

 stomodseum (fig. 4). Soon the left antero-lateral arm is involved and is pushed 

 over to the right (fig. 4). This is the first sign of the metamorphosis visible 

 to the naked eye. As metamorphosis proceeds, this left arm comes to lie close 

 to its fellow of the right side, and the first lobe of the hydroccele becomes 

 completely dorsal to the oesophagus. The left posterior coelom sends a 

 horn over to the right side beneath the oesophagus, and the posterior end 

 of the hydroccele extends over to the right, parallel to this horn, eventually 

 meeting the anterior end and converting the hydroccele into the water- 

 vascular ring. 



The movement of the anterior end of the hydroccele carries with it, as 

 already indicated, all the neighbouring parts of the animal, so that the pore- 

 canal and left anterior ccelom are carried over to the right and thus come into 

 close proximity with the right hydroccele, which occasionally, as is shown in 

 fig. 4, rJiy.j undergoes a development similar to that of the left side, presenting 

 five lobes. Often it presents two lobes, but normally it is a thin-walled 

 vesicle without lobes. 



