[huntsman] 



THE ASCIDIAN FAMILY CAESIRIDAE 



213 



Cope (1868, p. 272) was led to consider it possible that "one and 

 the same species (if origin be the definition), has, in the natural 

 succession, existed in more than one genus." With such a conception 

 the classification would not be expected to show the natural succsesion. 

 which might in the above case be as follows. 



In each of these arrangements parallel evolution is well shown. 

 In the former case there is the independent production of the corre- 

 sponding a, b and c species in the two genera, and in the latter case 

 the independent production of the X and Y generic characters in the 

 a, b and c lines of evolution. It is quite conceivable that both methods 

 of evolution have been followed, and that the species Yb has been 

 produced in two different ways, namely, by acquiring the generic 

 characters (Y) first and the specific characters (b) later, as in the 

 first scheme shown above; and by acquiring the specific characters 

 (b) first and the generic characters (Y) later, as in the second scheme. 

 The Mendelian phenomena of genetic segregation indicate that, if 

 this did occur, the final products in the two cases might be indis- 

 tinguishable. 



As the facts of parallelism prove that nearly related groups of 

 species have passed through almost identical evolutionary processes 

 in many instances, it is only reasonable to suppose that groups of 

 individuals all belonging to the same species still more frequently 



