142 MBST LESSONS IN ZOOLOGY. 



so to speak, an abortive attempt to reacli the yertebrate 

 level. It was given to some lonely worm, whose very fam- 

 ily name and form are now lost, to found a chain of being 

 whose links are now slowly, and with much painstaking 

 search on the part ^ of naturalists, being picked up and 

 brought to light. 



Even after the lancelet came into being, the steps by 

 which the genuine backboned family became recognized in 

 animal society were painful, and only in a degree successful 



Classes oj' Vertebrates. 



1. Toung with a nervous and dor- 

 sal cord Tunieata. Ascidians. 



3. No skull or brain; blood wbite -t«pfcif<wcZ««. Lancelet. 



3. Notocord persistent; no jaw- 



bones; six to ten pairs of 



purse like gills Maraipobranehii. ^Ijaxapteys. 



4. Swimming by fins; with gills; Y.?/(A<aAwV|y\./»A».' 



a movable under jaw Pisces. Fishes.r: ^^ff- ^^jaJ^"^^, 



5. Amphibious; true limbs and l^.'OiXxA\kj'^^ 



1 ungs ; skin smooth, no scales, J il Jjji>L/vx-o-v, 



no claws Batraehia. AmphiManBr Frog, etc 



6. Claws and scales present Beptilia. Snake, lizard. 



7. Body covered with feathers; 



fore-limbs forming wings. . .Aees. Birds. 



8. Body covered with hair; suck- 



ling their young Mammalia. Beasts. 



Literature. 



For works on Balanoglossus, see the essays of Kowalevsky, A. 

 Agassiz, and Bateson; also the latter's paper on the Ancestry of 

 Chordata in Quart. Journ. Micr. Science, 1886. 



For works on Amphioxus, — Bice : Observations upon the Habits, 

 Structure, and Development of Amphioxus lanceolatus (American 

 Naturalist, Jan. and Feb. 1880). Btieda : Studien ueber den Am- 

 phioxus lanceolatus (St. Petersburg, 1873). With the works of 

 MilUer, Kowalevsky, Hatschek, Langerhans, Lankester, etc. 



