SECT, xii PHYLUM CHORDATA 



1. TflV ADELOCHORDA 



Of somewhat doubtful relationships both to 

 one another and to the other Chordata are cer- 

 tain remarkable marine animals which have 

 been grouped together under the name of 

 Hemichorda or Adelochorda. These are 

 Balanoglossus &&& its allies, which occur in. 

 shaTjoy water on the coasts of rnnst of the 

 warmer parts of the world, ancJLtwo are deep- 

 sea animals, Rhabdopleura and Cephalodiscus. 



Balanoglossus (Fig. 195) is a soft-bodied, 

 cylindrical, worm-like animal, the surface of 

 which is uniformly ciliated. It is divisible into 

 three regions ^Lm front there is a large, club- 

 shaped, hollow organ the 



diately behind the proboscis and encircling its 



base is a prominent fold the collar ;(^jjf\o. 

 third region or trunk is long and nearly cylin- 

 drical, but somewhat depressed. 



Balanoglossus lives in the sea, burrowing 

 in sand or mud by means of its proboscis. It 

 occurs as far north as Salem, Mass., between 

 tide-marks. Numerous glands in the integu- 

 ment secrete a viscid matter to which grains 

 of sand adhere in such a way as to form a 

 fragile temporary tube. The proboscis (Fig. 

 195, pr, Fig. 196, proti) has muscular walls; 

 its cavity opens on the exterior usually by a 

 single minute aperture the proboscis pore 

 (Fig. 196, prob. po} rarely by two. The 

 collar (Fig. 195, cd) is 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 com- 

 municates with the exterior by a pair of collar 

 pores ciliated tubes leading into the first 

 gill-slit or first gill-pouch. 



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