134 



THE CHAIN OF LIFE. 



cartilaginous fishes, these must have continued for vast ages 

 without any elevation, and struggling for a bare existence 

 amidst formidable Cuttle-fishes and Crustaceans, before, under 

 more favourable conditions, they suddenly expanded into the 

 high and perfect types of Ganoids and Sharks. If we reject 

 the early Conodonts, then the two last-mentioned types spring 

 together and suddenly into existence, like the armed men from 

 the dragon's teeth of Cadmus. They rapidly attain to numbers 

 and grandeur unexampled in later times, and become the lords 

 of the waters at the time when there was probably no Vertebrate 



Fig. 122. — Modern Ganoids {_Polyptents. Africa. Lepidosteiis, A nerica). 



life on the land. As the reptiles establish themselves on the 

 land and in the waters, the Ganoids diminish, but the Sharks 

 hold their own. At length the reign of reptiles is over, but the 

 Ganoids, instead of resuming their pristine numbers, give place 

 to the Teleosts, and become reduced to insignificance ; while 

 the Sharks, profiting by the decadence of the great marine 

 reptiles, remain the tyrants of the seas. This history is 

 strangely unlike a continuous evolution ; but we are anticipa- 

 ting facts which will fall to be discussed in a subsequent 

 chapter. 



