No. 1.] THE DEVELOPMENT OF BALANOGLOSSUS. 75 
REFERENCE LETTER. 
b.c.1 Body-cavity, first. g2  Gill-slit, second. 
b.c.2 Body-cavity, second. n.c. Notochord. 
bc Body-cavity, third. p.v. Proboscis vesicle. 
f. Funnel or nephrostome of collar- | 4  Tongue-bar of gill-pouch. 
pores. 4.6. Tube of ectoderm leading to 
g' Gill-slit, first. mouth. 
