APPENDIX 189 



simplest case of the dorsal notochord, and paired pharyngeal slits 

 and arches. 



Subtype I. PROTOCHORDATA. Primitive or degenerate chor- 

 dates with worm-like bodies, withotit paired appendages, distinct 

 head, or special sense-organs, and with colorless blood. 



Class I. Hemichorda. Elongate protochordates with a large pro- 

 boscis or epistome in front of the mouth. Ex. Balanoglossus. 



Class II. Urochorda (Tunicata). Protochordates in which the 

 body is enclosed in a mantle and a tunic or test ; a ventral heart 

 is present ; tunicates. 



Order 1. PERENNICHORDA TA . Minute free-swimming tuni- 

 cates with a long tail. Ex. Appendicularia. 



Order 2. ASCIDIACEA. Mostly sessile, saccular tunicates. 

 Ex. Molgula. 



OrderS. THALIACEA. Free-swimming transparent tunicates 

 with cylindrical body. Ex. Salpa. 



Class III. Cephalochorda. Elongated, fish-like protochordates, 

 compressed laterally, and attenuated at both ends. Ex. Amphioxus. 



Subtype II. VERTEBRATA. Chordates with distinct head, bear- 

 ing organs of special sense, with red blood, and usually two pairs 

 of appendages. 



Class I. Pisces. Aquatic vertebrates with gills and without 

 lungs and usually with paired fins ; fishes. 



Class II. Amphibia. Vertebrates with gills during a part or all 

 of their life, and usually with lungs, with two pairs of legs, and 

 without scales ; amphibians. 



Class III. Reptilia. Vertebrates with body covered with horny 

 scales or plates, and without gills ; reptiles. 



Class IV. Aves. Feathered vertebrates whose anterior append- 

 ages are wings; birds. 



Class V. Mammalia. Hair-covered vertebrates which suckle 

 their young; mammals. 



