CHORDATA 



263 



lies in the region of the collar and proboscis; that the nervous 

 system is widely distributed over the bo< 

 the most highly differentiated portion lying 

 on the dorsal side of the collar, and that 

 there is a well-developed blood system and 

 body-cavity. The sexes are separate. In 

 some species the development is direct, in 

 others a larva is produced, called Tornaria 



-fir 



•ec 



-fir 



-ffVV 



rrvo 



eye 





; ^/cotrd.s 

 .'?■$ — -ftrob.pc 



~T — — irtb 



[Mi 



:iZ. j 



Cil.-r z 



FlG. 273. Tornaria, the larva of Balanoglossus. Lateral 

 aspect; magnified, an, anus; card.s, cardiac sac; cil.r, 

 post-oral ciliated band ; cil.r 2 , posterior ciliated ring; 

 eye, eye-spot on apical plate ; hit, intestine ; mo, mouth; 

 prob.po, proboscis pore. (After Spengel, from Parker and 

 Haswell's Text-book.) 



FlG. 272. Balano- 

 glossus. Dorsal as- 

 pect, br, branchial 

 region ; co, collar ; 

 gen, genital ridges ; 

 hep, elevations formed 

 by hepatic caeca ; pr, 

 proboscis. (After 

 Spengel, from Parker 

 and Haswell's Man- 

 ual.) 



(Fig. 273), which is much like the larva? of 

 the Echinodermata. 



The systematic position of Balanoglossus 

 is still in dispute : by some it is classified 

 with the worms ; by many it is believed to 

 be closely related to the Echinodermata be- 

 cause of its larva ; by the majority it is placed 

 with the Chordata. 



