ASYMMETRY IX THE STARFISH. 



119 



time and in the same manner in right-handed as in left-handed 

 larvae. 



The Form of Bipennaria and of Brachiolaria Larvce. The form 

 of the Bipennaria on the fifth day is shown in Fig. 9. It may be 

 noted that the blastopore or larval anus has moved around to a 

 distinctly ventral position ; that the hydropore and pore-canal are 

 well defined ; that the posterior coelom is now distinctly vesicular ; 

 and that both preoral and postoral ciliated bands have begun to 

 be differentiated. 



pr.l. 



/n. a c 



m 



r.a.c. 



l.p.C 



mt. 



-m 



oes. 



r.hyc. 



r.pc. 



IO II 



FIG. 10. Dorsal view of an advanced Bipennaria showing the ordinary left- 

 handed asymmetry. 



FIG. n. A somewhat more advanced Bipennaria seen from the dorsal side and 

 showing reversed or right-handed asymmetry- I'. p., hydropore; hyc., hydroccele; 

 int., intestine; /. a. c., left anterior coelom; l.h.p., left hydropore; l.p.c., left posterior 

 coelom; m, mouth; m.a.c., median anterior coelom; oes., oesophagus; pr.L, preoral 

 lobe; r.a.c., right anterior coelom; r.hyc., right hydrocoele; r.p.c., right posterior 

 coelom; st., stomach. 



At nine days the larva has undergone much change. The 

 right and left anterior coeloms have grown forward beyond the 

 mouth. The left (in reversed larvae, the right) anterior coelom 

 has extended backward so as to be in contact with the posterior 



