646 CHORD AT A. 



occur in other mammals. As they are fringed on the inner edges they 

 form a strainer which retains the small marine animals (plankton, Ceto- 

 chilns septentrionalis, a copepod, and Clione borealis, a pteropod) on which 

 these whales feed. The oesophagus is too narrow for the passage of 

 much larger animals. 



The origin of the whales is one of the unsolved problems. That they 

 came from some terrestrial, quadrapedal forms is beyond question, and the 



Fig. 669.— Section through jaws of whalebone whale. (After Delage.)^ c, septum of 

 nose: m, mouth cavity; mx, maxillary bone; 2^> premaxillary (hinder end); i\ 

 vomer ; ly, baleen. 



little evidence would seem to point to an ungulate or a carnivore ancestry. 

 It is possible th.at the toothed and whalebone whales may have had differ- 

 ent ancestries, and their resemblances may be the result of convergence. 



Sub Order I. ZEUGLODONTA. Extinct (eocene) forms with hetero 

 dont dentition, the posterior teeth two-rooted. 



Sub Order II. DENTIOET^, toothed whales, carnivorous, some hav- 

 ing but two teeth. Delphinus, dolphins ; Globioceplialus* black fish ; 

 Monodon, narwal, with, in the male, a long maxillary tusk (possible origin 

 of the 'unicorn'). Physeter macrocephahis, sperm whale, pursued for 

 the spermaceti, an oily mass situated in the ' chair' between the cranium 

 and the snout, as well as for ambergris, formed in the intestines. 



Sub Order III. MYSTACETI, whalebone whales, with baleen. Bala- 

 7ioptera,* rorquals and fin backs. B. sibhaldi,* the largest whale, reach- 

 i'lg a length of eighty-five feet. Balana, right whale. 



Order X. Carnivora. 



The carnivores live cliiefly on the flesh and blood of other ver- 

 tebrates, which they catch by craft, by coursing, or by pouncing 

 Tipon them, overpowering their prey by their sharp claws and 

 cutting teeth. With this mode of life correspond the high devel- 

 ojinient of the brain (fig. 64!), B) and sense organs, as well as 



