iga PRIMARY FACTORS OF ORGANIC EVOLUTION. 



burger and Buckman among Ammonitinae, and those 

 of Bather among crinoids, to designate the complete 

 study of the correlations of the ontocycle and phylo- 

 cycle as Bioplastology. Bioplastology is easily sepa- 

 rable from the study of growth, and from that of hered- 

 ity, for which last I have proposed the term Genesi- 

 ology, 1 and from that of Ctetology or the study of the 

 origin of acquired characteristics. By properly defin- 

 ing these different branches of research it is practicable 

 to see that bioplastology includes the results of the ac- 

 tion of growth, the laws of growth, as well as those of 

 genesiology and ctetology, but has a field entirely dis- 

 tinct from all of these in so far as it deals essentially 

 with the study of parallelism in all its phases. " 



The parallelism of the gyroceras with an early stage 

 of all coiled Cephalopoda is represented in Fig. 119 

 page 410, as illustrative of the inheritance of an ac- 

 quired character. 



3. PARALLELISM IN THE VERTEBRATA. 



Parallels between the ontogeny and phylogeny are 

 well known in the Vertebrata. The primary relations 

 of the Vertebrata are discernible in the successive 

 types of structure of the nervous system, and of the 

 skeleton, but most clearly in those presented by the 

 circulatory system. It is well known that the central 

 organ the heart, is, in the amphioxus, a straight 

 tube. In the next higher group, the Marsipobranchii 

 (lampreys), it is a bent tube, with a constriction which 

 divides it into two chambers. In the Pisces (fishes) 

 the heart is composed of two chambers related to each 

 other in a reversed longitudinal direction. In the Ba- 



1 See Proceedings of the Boston Society of Natural History, 1893, p. 59. 



