XII 



PHYLUM CHORDATA 



boscis (Fig. 182, /;-., Fig. 183, prob.} has muscular walls; its cavity 

 opens on the exterior usually by a single minute aperture the proboscis 

 pore (Fig. 183, prob. po. ) rarely by two. The collar (Fig. 182, co.) is 



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FIG. 183. Balanoglossus. Diagrammatic sagittal action of anterior end. card. s. 

 cardiac sac ; div. diverticulum (supposed notochord) ; dors. n. dorsal nerve 

 strand ; dors. sin. dorsal sinus : dors. v. dorsal vessel ; mo. mouth ; prob. pro- 

 boscis ; prob. po. proboscis pore ; prob. skel. proboscis skeleton ; vent. n. ventral 

 nerve strand ; vent. v. ventral vessel. (After Spengel.) 



also muscular, and contains one cavity or two (right and left) separated 

 from one another by dorsal and ventral mesenteries, and completely 

 cut off from the proboscis. The collar cavity communicates with the 



