130 BIOLOGICAL LECTURES. 



the same law of reproduction. If the old position is true, that 

 an organism when it evolves into another organism necessarily 

 gives rise to one like itself, then the evolution of a genetically 

 connected stock is an inevitable corollary of the existence of a 

 single organism endowed with the power of reproduction. If 

 phylogeny is a product or function of ontogeny, there is a nat- 

 ural basis for the correlations between these two classes of 

 organic movements, and their essential similarity is probably 

 due to this connection. ^ 



While this is obviously true, and one can describe the 

 phylogeny in parallel terms to those used for the ontogeny, 

 as is done further on, we should nevertheless bear in mind 

 certain essential distinctions. Thus, the genetic stock has not 

 the absolute continuity of the ontogeny. When regarded in 

 any living or fossil fauna it is an aggregate of organisms, 

 a mosaic of single life histories as distinctly separated from 

 each other in time and space as the pieces of mosaic, except 

 during the brief stage of parental connection. All the changes 

 and movements in phylogeny are necessarily based on two con- 

 ditions : first, the aspects of the faunas on any one level in 

 time, and second, the relations of series of these on successive 

 levels in time. The successive faunas on different levels, as 

 shown by the geologic history of any genetically connected 

 stock of phylum, resolve themselves into very definite series 

 of pictures characterized by distinct structural and physio- 

 logical changes. 



Both the ontogeny and phylogeny start from the same initial 

 point, and the divergencies necessarily take place first in the 

 ontogeny and are afterwards transmitted to the phylogeny. 

 This initial point for the organism is of course the Protozoan- 



^ Jackson, in his " Localized Stages in Development of Plants and Animals," 

 Mem. Boston Society of Natural Histo)y, vol. v. No. 4, 1S99, has lately added another 

 chapter to the correlations of ontogeny and phylogeny in showing that the twigs 

 and leaves of plants and plates of the echinoderms, or inflection of the septal edges 

 (sutures) of an Ammonite, or bud of an Actinozoon, etc., although arising from 

 or in the body of an adult organism, repeat the ontogenetic metamorphoses or 

 changes which occurred in similar parts that first arose in the early stages. He 

 has also applied this newly discovered phase of the ontogeny to the translation 

 of the phylogeny and the natural classification of groups. 



