604 



INVERTEBRATE MORPHOLOGY. 



The blood-spaces in the proboscis-gland communicate with 

 the heart, and the dorsal and ventral vessels of the collar and 

 trunk are united by a double set of fine lacunar capillaries, 

 one set being situated in the body-wall, and the other in the 



Fig. 375. — Transverse Sections through (A) the Proboscis and (B) the 

 Branchial Region op the Trunk of Balanoglossus Kowalewskii (B after 

 Spengel). 

 cop = collar-coelom. 

 g = tongue-bar of skeleton. 

 h = heart. 



kd = branchial valve. 

 kh — branchiiil portion of oesophagus. 

 ka = branchial septum. 

 kp = branchial pore. 



Im = longitudinal muscles. 

 no = notochord. 

 nd = dorsal nerve. 

 nv = ventral nerve. 



= CBsophagus. 

 pc = proboscis-coelom. 

 pg = proboscis-gland. 



ps = proboscis- vesicle. 



wall of the intestine. The blood is a colorless coagulable 

 fluid, apparently destitute of corpuscles. 



In the posterior portion of the proboscis is found a plate 

 of chitinlike material produced into two horns posteriorly, 

 and frequently' somewhat hollowed out in front. It is evi- 

 dently supportive in function, and forms the proboscis-skele- 

 ton. In connection with the branchial slits a similar chitinous 

 skeleton is formed (Fig. 276) consisting of a series of trans- 

 verse bars placed over each septum between adjacent slits. 

 From the middle of each bar a rod (really double) passes 

 down each septum (sb), and from the extremities a bar {tb) 

 passes into each of the adjacent tonguelike valves, each valve 

 thus possessing a bar from the arch lying in front of it and 

 another from that lying behind it. The septal bars and the 



