XVII 



PEOTOCHOEDATA 



643 



intestine are developed from a third bud, which arises from the old 

 oesophagus just where the epicardial bud joins it (Fig. 468, D) ; and 



Fig. 468. — Four stages in the budding of a Diplosomid Ascidian. (After Pizon.) 



A, the oozooid (i.e. the organism produced by the metamorphosis of the larva) has produced by 

 separate buds a new pharynx and oesophagus and a new intestine. B, the new organs [have greatly 

 increased in size. C, the pharynx of the oozooid is reduced to a degenerate mass, its oesophagus and 

 intestine have disappeared, but the second pharynx has produced by budding a third pharynx ; a second 

 stomachic loop has been produced. D, the third pharynx has increased in size and has developed an 

 oesophagus and a third intestine has been produced. A second heart has been produced from the second 

 pharynx, and the second stomachic loop has become functional, endst, endostyle ; ep, epicardial out- 

 growths from second pharynx ; Hj, H2, the hearts ; inU, int^, int^, the intestinal rudiments ; oes^, oes^, 

 oes^, the oesophageal rudiments ; ph^, ph% pK^, the three pharynges ; s(i, st^, the two stomachs.' 



SO a compound organism arises with two branchial sacs joining in a 

 common gut, which then bifurcates into two intestinal buds, which 

 reunite at their distal ends, only to bifurcate again into two recta. 



