PHYLUM CHORDATA 



325 



Mouth cavity 

 Brain— I 



Gill slit -| 

 Pharynx 



Pancreas 



Kidney 

 Gonad 



Genital duct 

 Ureter 



Remnant of notochord 



Nerve cord 



Vertebra 



Pericardial covity 

 Esophagus 



Cloaca 

 Cloacal opening 

 Urinary bladder 

 Coelom 



'-Spleen 

 ntestine 



Figure 208. 

 structure. 



Stomach—' Bile duct-" 

 A longitudinal vertical section of a generalized vertebrate, showing the plan of 



maeras. Cold-blooded vertebrates 

 with jaws, a cartilaginous skeleton, 5 

 to 7 pairs of gills in separate clefts, a 

 persistent notochord, placoid scales, 

 and paired fins. 



Class 3. Osteichthyes (Gr. osteon, bone; 

 ichthys, fish). Fishes (Fig. 200). 

 Cold-blooded vertebrates with jaws, 

 bony skeleton, 4 pairs of gills in com- 

 mon cavity under opercula, skin usu- 

 ally with cycloid or ctenoid scales, 

 usually with paired fins. 



Class 4. Amphibia (Gr. amphi, both; bios, 

 life). Frogs, toads, and salamanders 

 (Fig. 200). Cold-blooded vertebrates, 

 skin moist, no external scales, mostly 

 with pentadactyl (5-fingered) limbs; 

 young usually aquatic and breathe by 

 gills; adults usually lose the gills and 

 breathe by means of lungs. 



Class 5. Reptilia (L. repere, to crawl). Tur- 

 tles, sphenodon, lizards, snakes, and 

 crocodiles (Fig. 200). Cold-blooded 

 vertebrates breathing by means of 

 lungs and usually having a dry scaly 

 skin; respiration always by lungs. 



Class 6. Aves (L. avis, bird). Birds (Fig. 

 200). Warm-blooded vertebrates 

 with the forelimbs modified into 

 wings and the body covered with 

 feathers. 



Class 7. Mammalia (L. mamma, breast). 

 Hairy quadrupeds, whales, squirrels, 

 bats, monkeys, and man (Fig. 200). 

 Warm-blooded vertebrates with a 

 hairy covering at some stage in their 

 existence; the young nourished after 

 birth by the secretion of the mam- 

 mary glands of the mother. 



SELECTED COLLATERAL 

 READINGS 



Berrill, N.J. The Origin of Vertebrates. Claren- 

 don Press, Oxford, 1955. 



Bullock, T.H. "The Anatomical Organization 

 of the Nervous System of Enteropneusta." 

 Quar. J. Microscop. Sci., 86:55-111, 1945. 



Carson, R.L. The Sea Around Us. Oxford 

 Univ. Press, New York, 1951. 



Morgan, T.H. "The Development of Balano- 

 glossus." /. Morphol. and Physiol, 9:1-86, 

 1894. 



Ritter, W.E., and Davis, B.M. "Studies on the 

 Ecology, Morphology and Speciology of the 

 Young of Some Enteropneusta of Western 

 North America." Univ. Calif. Pub. Zool., 

 1:171-210, 1904. 



Willey, A. Amphioxus and the Ancestry of the 

 Vertebrates. Columbia Univ. Press, New 

 York, 1894. 



