142 FIRST LESSONS IN ZOOLOGY. 



so to speak, an abortive attempt to reach the vertebrate 

 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 OF VERTEBRATES. 



1. Young with a nervous and dor- 



sal cord Tunicata. Ascidians. 



2. No skull or brain; blood white Leptocardii. Lancelet. 



3. Notocord persistent; no jaw- 



bones; six to ten pairs of 



purse like gills Marsipobranchii. Lampreys. 



4. Swimming by fins; with gills; 



a movable under jaw Pisces. Fishes. 



5. Amphibious; true limbs and 



lungs; skin smooth, no scales, 



no claws Batrachia. Amphibians. Frog, etc. 



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



7. Body covered with feathers; 



fore-limbs forming wings. . .Aves. Birds. 



8. Body covered with hair; suck- 



ling their young Mammalia. Beasts. 



