6f.$ 



Ruatt Liter 



[August, 



our existing crayfishes, of which the accompanying figures are 

 examples, and we shall see how deeply planted are the roots of 

 the astacine genealogical tree, which extends down into Jurassic 

 strata. Finally we are told by our author that all modern cray- 

 fishes have evolved from such forms as the Pseudastacus. 



And here it seems to us singular that Professor Huxley, while 

 stating his belief that all crayfish have evolved from earlier forms, 

 should not have attempted an explanation of the causes of change 

 of form and of the variability which has resulted in the produc- 

 tion of species of crayfish on all the continents. Why did he not 

 avail himself of the published facts concerning our Mammoth 

 nd blind species, and discuss the effects of darkness and 



an blind form, 

 auses, of the differ- 

 ences in the nature of streams and food supply would have been 



the causes of the evolution of forms so rich in species and varie- 

 ties as our crayfish, a fact which in this country at least renders 

 their systematic study so perplexing. 



There is little, however, to criticize in this as in all of Professor 

 Huxley's works. They are critical as well as broad and philo- 

 sophical. 



We would however venture to take exception to Huxley's con- 



