PLATE XXV 1 1. 



Class-HEMICHOKDATA. 



Balanoglossus. 



FIG. 1. BALANOGLOSSUS MINUTUS: DORSAL VIEW, x 1. 



p. proboscis : c. collar : b. branchial region : g. gastric region : t. tail 

 region : d. dorsal vessel : a. anus. 



FIG. 2. BALANOGLOSSUS SARNIENSIS ; ANTERIOR END : DORSAL VIEW, x 1. 



FIG. 3. TRANSVERSE SECTION THROUGH THE MIDDLE OF THE BRANCHIAL PORTION 

 OF BALANGLOSSUS MINUTUS. x 8. 



&. branchial arch : p., p. constricted pharynx : d. dorsal opening in the 

 pharynx : 1. 1. lateral lobe, in which the generative glands lie : 

 Ir. lateral blood-vessel : Ig. longitudinal ventral blood-vessel. 



FIG. 4. TORNARIA LARVA : DORSAL VIEW. (After Metschnikoff.) 

 w. water vessel : h. heart : p. peritoneal sac. 



FIG. 5. STAGE IN THE GROWTH OF TORNARIA INTO BALANGLOSSUS : SIDE VIEW. 

 (After Metschnikoff.) 



m. mouth : h. heart : v. circular vessel : &. external branchial opening. 



FIG. 6. MORE ADVANCED STAGE. (After Agassiz.) 



w. water vessel : h. heart : m. mouth : Z>. external branchial slits. 



FIG. 7. STILL MORE ADVANCED STAGE. (After Pagenstecher.) x 12. 



