78 CALIFORNIA ACADEMY OF SCIENCES. 



that species naturally arrange themselves into series in 

 consequence of a mathematical order of excess or defi- 

 ciency in some feature or features. Thus species with 

 three toes naturally intervene between those with one 

 and four toes. ^ * ^ 



" 3. Parallidism. This states that while all animals in 

 their embryonic and later growth pass through a num- 

 ber of stages and conditions, some traverse more and 

 others traverse fewer stages; and that, as the stages are 

 nearly the same for both, those which accomplish less 

 resemble or are parallel with the young of those which 

 accomplish more. * •5'- -^ 



' ' 4. Teleology. This is the law of adaptation so much 

 dwelt upon by the old writers, and admired in its ex- 

 hibitions by men generally. It includes the many cases 

 of fitness of a structure for its special use, and expresses 

 broadly the general adaptations of an animal to its home 

 and habits." 



5. Geratology. Prof. Hyatt has enunciated this 

 principle of distorted or pathological types.* It is the 

 law that there " is an exact correspondence between the 

 life of an individual and the group to which it belongs : 

 namely, the young and adolescent stages having direct 

 correspondence and repeating the past history of its 

 own group to a greater or less extent, the adult corre- 

 sponding to the present with all the peculiarities and 

 differences of its group, and the metamorphoses of old 

 age to the pathological modifications and changes found 

 in the types which arose in the unfavorable localities, or 

 which were found as a rule to terminate the history of 

 the group in time." 



To this list may be added the following special laws 

 of structure, both of which may be more or less closely 

 related to homology: 



* Proc. A. A. A. S., xxxii, p. 349. 



