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MANUAL OF ZOOLOGY 



On the dorsal surface of the anterior part of the trunk is a double 

 row of small slits — the gill-slits (Fig. 195, /</-,) — each row situated in 

 a longitudinal furrow; these slits increase in number throughout. The 



Fig. 196. — Balanoglossus. Diagrammatic sagittal section of anterior end. card, 

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

 strand; dors, sin, dorsal sinus; dors, v, dorsal vessel; vio, mouth; prob, pro- 

 boscis; prob. po, proboscis pore; prob. skel, proboscis skeleton; vent, n, ven- 

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



ccelom of the trunk is divided into two lateral closed cavities by a verti- 

 cal partition (dorsal and ventral mesenteries). 



The mouth (Fig. 196, mo,) is situated ventrally at the base of the 

 proboscis, within the collar. Into the dorsal half of the anterior portion 



