181 



ZOOLOGY. 



f these primitive types that the leading divisions of the 

 animal kingdom are established. 



352. Natura nonfacit saltum, was the ancient adage: 

 its truth is exemplified by the history of the animal kingdom. 



Fig. 122. Craw-fish or Lobster.* 



Fig. 123. Masticatory Apparatus. 



The change from one form of organization to another is never 

 sudden, but, on the contrary, takes place gradually, and as it 

 were by shades of difference. 



* Fig. 122. The lobster or craw-fish, seen from below : a, antennae of the 

 first pair ; b, antenna; of the second pair ; c, the eyes ; d, the auditory 

 tubercle; , mandible feet, external ; f, thoracic feet of the tir>t pair ; </, 

 thoracic feet of the fifth pair; h, false abdominal feet ; i, caudal fin .- J, anus. 



Fig. 123. The six pairs < f limits which compose \\\>- in.oii, atory apparatus 

 of the lobster or craw-fish ; a, mandibles ; b, e, first and second pairs of 

 jaws ; rf, e,f t the three pairs of auxiliary jaws or foot-mandibles. 



