3io 



MANUAL OF ZOOLOGY 



SECT. 



presence at all stages, or only 

 in the larva, of a cavity or 

 system of cavities, the neuro- 

 Cttle y in the interior of the 

 central nervous system. 



FIG. 182. BalanoglOSSUS Entire ani- 



1. THE ADELOCHORDA 



Of somewhat doubtful relation- 

 ships both to one another and to 

 the other Chordata are certain re- 

 markable marine animals which 

 have been grouped together under 

 the name of Adelochorda or Hemi- 

 chorda. These are Balanoglosstis, 

 which occurs in shallow water on the 

 coasts of most of the warmer parts 

 of the world, and two rare deep-sea 

 animals, Rhabdopleura and Cepha- 

 lodiscus. 



Balanoglossus (Fig. 182) is a soft- 

 bodied, cylindrical, worm-like ani- 

 mal, the surface of which is uni- 

 formly ciliated. It is divisible into 

 three regions : in front there is a 

 large club-shaped hollow organ the 

 proboscis ; immediately behind the 

 proboscis and encircling its base is a 

 prominent fold the collar ; the third 

 region or trunk is long and nearly 

 cylindrical, but somewhat depressed. 



Balanoglossus lives in the sea, 

 burrowing in sand or mud by means 

 of its proboscis. Numerous glands 

 in the integument secrete a viscid 

 matter to which grains of sand ad- 



mal. br. branchial region ; co. collar ; r 



gen. genital ridges; hep. promi- here in such a way as t< 

 nences_ formed by hepatic csca ; fra{T i] e temoorarv tube. 



pr. proboscis. (After Spengel.) 



fragile temporary tube. The pro- 



