No. 6. — Studies in Morphogenesis. — IV. A Preliminary Cat- 

 alogue of the Processes concerned in Ontogeyiy.^ By C. B. 

 Davenport. 



contents. 



Page 

 Introduction : Limitations of the Paper 173 



A. General Ontogenetic Processes 174 



B. Special Ontogenetic Processes 174 



I. Ontogenetic Processes occurring in Migratory Protoplasmic Bodies 



(Mesenchyme) 175 



II. Ontogenetic Processes occurring in Elongated Protoplasmic Bodies 



(Fibres, Threads, Cords, Tubules) 180 



III. Ontogenetic Processes occurring in Protoplasmic Layers .... 184 



IV. Ontogenetic Processes occurring in Protoplasmic Masses .... 192 

 Recapitulation and General Kemarks 196 



Most important perhnps of all the problems which the biologist sees 

 lying nnsolved before him is that of the development of the individual, 

 — a problem to which, from the time of Aristotle, zoologists have re- 

 peatedly turned, although scarcely hoping for its eventual solution. 



Without attempting to consider the various theories of Ontoniorpho- 

 genesis which have at different times been offered, it is sufficient to state 

 that it is now generally agreed that ontogenesis is a process, or rather a 

 complex of processes, taking place in the protoplasm of the developing 

 individual. 



Now it is a highly probable belief that no movement takes place in 

 protoplasm except as a response to stimuli. The very fact that onto- 

 genesis is a complex of actions indicates that there must be a large 

 number of stimuli raining in upon the different parts of the developing 

 protoplasm to which they respond. 



In order to gain some idea of what the stimuli are, it is first neces- 

 sary to analyze the ontogenetic complex of processes into its simple 

 elementary ones. 



It is the aim of this paper to make such an analysis into the elemen- 

 tary ontogenetic processes as a basis for determining the nature of the 

 exciting stimuli. 



1 Contributions from the Zoological Laboratory of the Museum of Comparative 

 ZoiJlogy at Harvard College, E. L. Mark, Director, No. L. 



VOL. XXVII. — NO. 6. 1 



