XVII 



PBOTOCHOKDATA 



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 



oes' 



FIG. 468. Four stages in the budding of a Diplosoniid 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 ihave 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 ; HI, H%, the hearts ; infl, inft, int 3 , the intestinal rudiments ; oes 1 , oes 2 , 

 ties 3 , the oesophageal rudiments ; phi, ph 2 , ph s , the three pharynges ; sfl, st 2 , 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. 



