204 



ZOOLOGY. 



passes from one type to another. By reason of these circum- 

 stances, it is also impossible to arrange animals in a single 

 linear series, without violating at every instant their respective 



Fig. 157. Cyclops, one of the 

 Entomostraca. 



Fig. 155. Lernsea. 



Fig. 158. Larvse of the Cyclops. 



affinities, and we are obliged to disperse them into several 

 parallel lines, or lines branching out from each other. 



[Such relations being based on embryology, which again rests 

 on the transcendental, must be used with great caution, and 

 must not be mistaken for any natural generic or specific consan- 

 guinite between the animals forming the subject of observation. 

 The young of the Balanus, or acorn- shell, whilst in the larva state, 

 also closely resembles the Entomostraca (microscopic shell-fish) 

 as well as that of the Lerncece. In a philosophic sense, however, 

 such observations are, notwithstanding, exceedingly interesting ; 

 and they tend to show that animals which we have hitherto con- 

 sidered as adult, specific, and fully developed, may after all be 

 merely "arrested forms" of others passing through various 

 metamorphoses. B. K.] 



367. The second condition in the establishment of a 

 natural classification is an exact relation between the suc- 

 cessive divisions of the animal kingdom and the importance 

 of the modification of structure serving as the basis to these 

 sections. 



