VIII.] UOMOLOGIES. 185 



the same niay be said of every single arthropod and annelid 

 if it be meant that all these organs are not contained in 

 every possible slice. While if it be meant that parts of all 

 such organs are contained in certain slices, then some of the 

 mollusca may also be included. 



Another objection to Mr. Spencer's speculation is de- 

 rived from considerations which have already been stated, 

 as to past time. For if the annulose animals have been 

 formed by aggregation, we ought to find this jirocess much 

 less perfect in the oldest form. But a comj)lcte develop- 

 ment, such as already ol)tains in the lobster, etc., was 

 reached l)y ihe Euryptcrida and Trilobites of the j)al;ro7oic 

 strata; and annelids, probably formed mainly like those of 



TEn-OBITK. 



the present day, abounded during the deposition of the 

 oldest fossiliferous rocks. 



Thirdly, and lastly, as regards such serial liomology as 

 is exemplified by ihe backbone of man, there arc also sev- 

 eral objections to Mr. Spencer's mechanical exj^lanation. 



On the theory of evolution most in favor, the first Ver- 

 tebrata were aquatic. Now, as natation is generally effected 

 by repeated and vigorous lateral flexions of the body, we 

 ought to find the segmentation much more complete laterally 

 than on the dorsal and ventral aspects of the spinal column. 



