ZOOLOGY. 



THE VERTEBRATA. 

 PHYLUM VERTEBRATA OR CHORDATA. 



State the Chief Features of the Vertebrata or Chordata. 



The body is supported by an - internal skeleton (endo- 

 skeleton), the main axis of which is the dorsal notochord, an 

 elastic rod developed from the dorsal wall of the enteron. 

 In the higher Vertebrates, the notochord is replaced (in 

 the adult) by a more rigid vertebral column or segmented 

 backbone. 



Gill-slits or visceral clefts, with cilia or with gills, for 

 aquatic respiration, are formed in the wall of the pharynx 

 (the first part of the alimentary canal), and open indirectly 

 or directly to the outside. In Reptiles, Birds, and Mammals 

 the gill-clefts are present during embryonic life, but are 

 not functional as breathing organs. 



The central nervous system (brain and spinal cord) is 

 tubular and dorsal. The eye is mainly an outgrowth from 

 the brain. The heart is ventral. 



A Classification of the Vertebrata overleaf, 



SUB-PHYLUM ENTEROPNEUSTA OR HEMICHORDA. 



Balanoglossus or Dolichoglossus. 

 Give a general Description of Balanoglossus. 



The Balanoglossida ( Balanoglossus and others) are worm- 

 like and marine, mostly littoral forms which burrow in 

 sand or mud. The soft skin (epidermis) is ciliated, and 

 secretes much mucus. The body (from 1 to 6 inches, or 

 more, in length) consists of a conical expansible proboscis 

 (the preoral lobe) connected by a small constriction or 

 neck to a short thickened " collar," which is followed by 

 a long trunk. The mouth is ventral, between the proboscis 

 and collar. On each side of the front part of the trunk there 

 is a row of branchial pores ; these are the external openings 



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