194 



ZOOLOGY.. 



of these primitive types that the leading divisions of the 

 animal kingdom are established. 



352. Natura nonfacii saltum, was the ancient adage: 

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



Fig. 143. Crawfish.* 



Fig. 144. 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. 143. The lobster, or crawfish, seen from below : a, antennae of the 

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

 tubercle ; e, mandible feet, external ; f, thoracic feet of the first pair ; g, 

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



Fig. 144. The six pairs of limbs which compose the masticatory apparatus 

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

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



