THE DEVELOPMENT OF ASTBEINA GIBBOSA. 233 



septum dividing the two portions of thecoelom from each other 

 become again closed during the metamorphosis. 



The left hydroccele has become much more sharply separated 

 from the anterior coelom than in the last stage, though in the 

 region of the third lobe the hydroccele still opens widely into 

 the anterior coelom (PI. XII, figs. 38— 41; PI. XIII, figs. 44— 

 46). We saw that the pore-canal in Stage B originated a little to 

 the left of the middle line ; now, however, owing to the in- 

 creasing predominance of the left side, it is shifted to the right 

 of the median plane {pc, fig. 44). The stone canal {stc, figs. 

 45 and 46) arises as a groove along the anterior face of the 

 transverse septum forming the hinder wall of the anterior 

 coelom. The central portion of this groove soon becomes closed 

 to form a canal, opening at one end into the hydroccele between 

 lobes 1 and 2 (fig. 46), and at the other into the anterior ccelom 

 (fig. 45); and this opening is in this stage entirely inde- 

 pendent of the opening of the pore-canal. 



I have referred more than once to the predominance of the 

 organs of the left side. This is strikingly shown in the stage 

 we are considering by the narrowness of the right posterior 

 coelom as compared with the left. Already in Stage B we have 

 seen that the left posterior coelom has begun to sweep round 

 to the right on the ventral side of the right posterior coelom ; 

 this occurs more and more, and in the stage we are considering 

 in the most ventral sections (fig. -41) the right posterior coelom 

 is entirely absent. The left not only passes under it, but to a 

 certain extent interposes between its anterior portion and the 

 gut (figs. 39 and 40), and here opens freely into the anterior 

 coelomi (fig. 40) by the secondary ventral communication de- 

 scribed above. This portion of the left ccelom we may call its 

 right ventral horn ; it plays a most important part in the meta- 

 morphosis, and it is marked I'/c'. in all the figures. 



Ludwig failed entirely to recognise the left posterior coelom 



1 I may anticipate a little by informing the reader that the anterior ccelom 

 gives rise to the axial sinus of the adult ; a space which opens to the exterior 

 by the pore-canal and into the left hydroccele (water-vascular ring) by the 

 stone-canal. 



