103 



Coming now to the consideration of the third point, I may re- 

 mark that Goto's mistake as to the origin of the right hydrocoele is 

 due to two circumstances viz., first, he has not seen the earliest stages 

 in its development and secondly he has not recognized the true nature 

 of the division of the coelom. — Figure (2) which shows the inception 

 of the right hydrocoele, should I think convince any unprejudiced person 

 that it is an organ belonging to the right side. On each side the trans- 

 verse septum has been formed; in the morphological middle line the 

 gut is still in open communication with the anterior coelom and to 



Left 'posterior Coelom 



Anterior Coelom 



Bight Hydrocoele 



Right posterior Coelom 



fig. 2. 



the right of this the right hydrocoele is seen in process of being 

 budded off from the anterior coelom. 



The figures which Goto gives in order to prove the origin of this 

 organ show it in an already advanced state of development: at this 

 stage it has no real connection with any coelomic space, as Goto 

 would have seen had his specimens been will preserved. 



Having shown the mode of origin of the right hydrocoele the 

 only additional proof of its nature which could be adduced would be 

 to show that it occasionally underwent a similar development to that 

 of its fellow on the left side. This proof was already furnished by me 

 in my paper on the development of Asterina gibbosa. Figure (3) re- 

 presents a larva not then described in which the right hydrocoele is 

 large and thick-walled and has the histological characters of the left 

 hydrocoele. It shows a tendency to become divided into two lobes. On 

 the left side the dorsal gap in the left transverse septum can be seen. 



