362 TEXTBOOK OF ZOOLOGY 



Yertehrata (ver te bra'ta, jointed) animals with backbone — frog, 

 man. These are the larger, more conspicuous animals and will be 

 discussed at length in later sections of the book. 



Phylogenetic Advances of Chordata 



(1) Notochord and endoskeleton, (2) pectoral and pelvic girdles 

 with limbs, (3) development of dorsally located nerve cord with 

 anterior brain, (4) development of five senses, (5) pharyngeal gills 

 and lungs for respiration, (6) voice production, (7) specialization 

 and coordination of muscles. 



Protochordata (Lower Chordates) 



Until relatively recent years the two subphyla, Hemichorda and 

 Urochorda were not classified as Chordata; the former was with An- 

 nelida and the latter was independent. With the exception of the 

 value as biological specimens and the use of amphioxus as food by 

 Chinese, this group is of no economic importance. 



SUBPHYLUM HEMICHORDATA 



One of the species of Balanoglossus or Dolichoglossus koivalevskii 

 will serve as an example. They are wormlike animals which burrow 

 into the mud and sand along the seashore. They range from 6 to 10 

 inches in length. Others of the subphylum may be as short as one 

 inch or still others as long as four feet. The three portions of the 

 body are proboscis, a ringlike collar, and a segmented trunk. The 

 proboscis, as well as the collar, is hollow and serves as a water cham- 

 ber. The cavity of the proboscis is filled with water which is dra"wn 

 in and expelled through a proboscis pore or vent located on its dorsal 

 side and just anterior to the collar. Supporting the base of the 

 proboscis is a short skeletal process which is stiff and extends ante- 

 riorly from the roof of the mouth region and assists in burrowing. 

 This process, called the diverticulum, is usually referred to as the 

 rudimentary notochord. However, it is very poorly developed and 

 in a peculiar position. Nevertheless, it has the relationship to the 

 digestive tube which is characteristic in the embryonic development 

 of the notochord for certain higher chordates. The mouth opens on 

 the ventral side just anterior to the collar and leads into the straight 

 alimentary canal which extends to the posterior end of the body 



