164 



THE AMERICAN NATURALIST 



insect-like representatives of the ancestral isopods, while 

 the Symphyla-like members of the ancestral-insectan 

 group must have resembled the most insect-like repre- 

 sentatives of the ancestral Symphyla. In other words, 

 at the common level at which the lines of descent of the 

 isopods, insects and Symphyla originated, some of the 

 ancestral insects (which differed greatly among them- 

 selves) occupying the ''hereditary territory" contiguous 

 to that of the ancestral Symphyla would inherit certain 

 develo])mental tendencies in common with or similar to 

 those also inhei'itcd by certain Symphyla; and similarly, 

 some of the ancestral insects occupying the "hereditary 

 territory" contiguous to that of the ancestral isopods 

 would inherit certain developmental tendencies similar 

 to those of certain isopods and the same principle would 

 ai)])ly to successively larger, as well as to the smaller 

 groups in any evolutionary study. According to this 

 view, certai]! developmental or "inherent" tendencies 

 exhibited by the isopods or myriopods might also appear 

 in insects if the op]:)ortunity of manifesting themselves 

 should arise, and this would merely imply that these 

 tendencies were inlieritcd from an ultimately common 

 ancestry,- rather than that some insects were descended 

 from isopods while other insects wore descended from 

 Syni])hyln. etc. Some evolutionists might object to the 

 u.>e of Mich tenns as "inherent tendencies" on the ground 

 that they >av()i- too strongly of "vitalism"; but, so far 

 as 1 can see, tlie expression "inherent tendencies" means 

 much the same thing as a part of "heredity," and one 

 implies no more of a i)redilection toward vitalism than 

 the other does. 



Althongh their cio^o^t affinities are with the Cam- 

 p()<1i'f)I(l gr<Mij) an<l the A ] iIo'n uota in general, certain 

 inenilM'i'> of th(^ I.opi-iiioid uroiij) .-iro sj ructurally remark- 

 ably sintihn- in many rr^iic.-i^ 1o snch primitive Ptery- 



