PROTOCHORDATA 663 



the collar and trunk segments each in two lateral halves. (The trunk 

 cavities send forward into the collar a pair of " perihaemal " pro- 

 longations at the sides of the dorsal blood vessel, mentioned below.) 

 A pair, left and right, or a single, \th, proboscis pore opens at the base 



.Irk. 



Fig. 463. A Dolichoglossiis kozvalevskii, x i. From Spengel. 

 col. collar; M. mouth; pro. proboscis; sit. gill slits; trk. trunk. 



of the organ. The mouth opens on the ventral side, between the over- 

 lap of the collar and the proboscis stalk. A pair of collar pores open 

 backward from the collar cavities into the first gill pouch (see below). 

 Dorsolaterally on the first part of the trunk is on each side a row of 



