346 



EVOLUTION AND ANIMAL LIFE 



Entirely different are the photophores in the midshipman or 

 singing fish (Porwhthys) , a genus of the toad fishes or Batra- 

 choididse. These species live near the shore and the lumi- 

 nous spots are outgrowths from pores of the lateral line. 



In one of the anglers (Corynolophus reinhardti) the com- 

 plex bait is said to be luminous, and luminous areas occur 



on the belly of a very 

 small shark of the deep 

 seas of Japan (Etmopterus 

 ludfer). Dr. Peter Schmidt 

 of St. Petersburg has a 

 drawing of this shark 

 made at night from its 

 own light. 



While among the 

 higher or vertebrate ani- 

 mals, especially the fishes 

 and reptiles, most remark- 

 able cases of adaptations 

 occur, yet the structural 

 changes are for the most 

 part external, usually not 

 affecting fundamentally 



the development of the internal organs other than the skeleton. 

 The organization of these higher animals is much less plastic 

 than that of the invertebrates. In general, the higher the 

 type the more persistent and unchangeable are those struc- 

 tures not immediately exposed to the influence of the struggle 

 for existence. It is thus the outside of an animal that tells 

 where its ancestors have lived. The inside, suffering little 

 change whatever the surroundings, tells the real nature of the 

 animal. 



FIG. 208. Nest of the trapdoor spider. 



