III.] INDEPENDENT SIMILARITIES OF STRUCTURE. 93 



the curious similarity between a true mouse {Mus deli- 

 catidus) and a small marsupial, poiutecl out by Mr. Andrew 

 ]\Iurray in liis work on the " Geographical Distribution of 

 Mammals ;" but instances enough for the present purpose 

 have been already quoted. 



Cr^ 





'-^ 



w^ 



Upper Figure — Antechninus minutissimus (implacental). 

 Lower Figure — 'M.vs delicatulus (placental). 



Additional reasons for believino- that similarity of struc- 

 ture is produced by other causes than merely by " Natural 

 Selection " are furnished by certain facts of zoological 

 geography, and by a similarity in the mode of variation 

 being sometimes extended to several si:)ecies of a genus, 



