SITUS INVERSUS IN ECHINOIDS 



128 



definitely-recorded case belonging to this category is lacking. 

 By the kind permission of Professor MacBride I examined 

 his preparations and found among twenty whole mounts only 

 a single specimen with the right echinus-rudiment larger than 

 that of the left side. [Case 9.] 



Text-fig. 3. 



.-am 



Transverse sections of a fifteen-day-old double-hydrocoele larva 



of Echinus miliar is, in which the water-vascular system 



of the left side has begun to degenerate, x 300. 

 am, amniotic invagination ; ax, axial sinus ; dp, dp , dorsal pores ; 



g, stomach ; hy, hy , hydrocoeles ; mv, madreporic vesicle ; 



oe, oesophagus ; pc, pore-canal ; st, st', stone-canals. 



[Case 10.] Echinus miliar is. Culture 9, 'treated'. 

 This larva was found to have double hydrocoele when fifteen 

 days old, and then killed and examined by means of sections 

 (Text-fig. 3). 



Left : Axial sinus quite reduced, being represented by 



NO. 261 K 



