of the Costce in the Peris phinctince. 455 



number of skeletons ranging in age from young to adult 

 but all representing one species. Even in such a rare 

 and happy case there is no proof that the young indi- 

 viduals are actually the immature forms of the adults 

 found in the same place, however perfect a gradation in 

 characters and proportions may be shown in the speci- 

 mens, for parallelism in the development of genetically 

 unrelated species may so obscure the true diversity in 

 origin that an ideal series may be arranged which unfor- 

 tunately has no other value than its diagrammatic clear- 

 ness. It is even worse when the young individuals of 

 a species are found in a locality at some distance from 

 that where the adults occur. When we consider the 

 vicissitudes attending the preservation of vertebrates, 

 particularly terrestrial and aerial forms, when we think 

 of the many groups which must at all times have been 

 branching off from the main lines and have been develop- 

 ing progressively and retrogressively with changing 

 proportions and newly appearing characters, the chances 

 are rather against there being any necessary genetic 

 relationship between a young individual found at one 

 locality and an adult found at some distance, even if at 

 the same horizon. With organic and inorganic factors 

 working, it would seem, for the very purpose of obscur- 

 ing genetic relations, the vertebrate paleontologist cer- 

 tainly has no enviable task in trying to decipher ontogeny. 

 We see, then, that in this field the illustrations of ortho- 

 genesis must be sought almost wholly in phylogeny and 

 it is here that we find such celebrated series as those of 

 the horse, the elephant and the titanotheres. Yet is it 

 not true that in all of these cases there are elements of 

 doubt? We may not go so far as does Professor Morgan 

 who says that the paleontologist chooses to arrange his 

 specimens in certain series, but that they might just as 

 well be arranged in some altogether different fashion. 

 Thus, Professor Morgan has obtained in a single genera- 

 tion of flies what appears to be a perfect orthogenetic 

 gradation of eye color which makes a good series with 

 every transition shown from white to red and yet this 

 is due simply to certain slight differences in the chromo- 

 somes which produce in a single batch of flies variations 

 indicating no definite direction in development such as 

 a paleontologist would think he had if he found a series 

 showing similar slight gradations in a given character. 



