CHORDATA. 



With notochord, dorsal nerve cord, and branchial clefts dur- 

 ing some period of existence. 



Sub-phylum 1. Adelochorda. 



Body somewhat worm-like and divided into pro- 

 boscis, collar, and trunk. Notochordal devel- 

 opment slight. 

 Class Adelochorda. 



Characters as above. (Balanoglossus.) 

 Sub-phylum 2. Urochorda. 



Adult body inclosed in a tunic. Larvae usually 

 motile. Notochord confined to the tail region. 

 Class Urochorda. 



Characters as above. 

 Order 1. Larvacea. 



Swim throughout life by means of a tail. The 

 pharynx has a single pair of branchial slits. 

 (Appendicularia.) 

 Order 2. Thaliacea. 



Swim by forming currents of water. The pharynx 

 has tw^oor many branchial slits. (Salpa, Dololium.) 

 Order 3. Ascidiacea. 



]\Iostly fixed. Pharynx large, provided with 

 many branchial slits. (^Molgula, Perophora, Bo- 

 tr3^11us, Amaroecium.) 

 Sub-phylum 3. Vertebrata. 



Notochord or vertebral column present in the 

 adult practically throughout the length of the 

 body. Central nervous system forms a dorsal 

 nerve tiibe. 

 Division 1. Acrania. 



Without true skull or highly complex brain. 

 Class 1. Acrania. 



Characters as above. (Amphioxus.) 

 Division 2. Craniata. 



With true skull and highly developed brain. 

 (Six Classes and as many as fifty-six Orders may be recog- 

 nized under this Division.) 



164 



