174 BULLETIN : MUSEUM OF COMI'AKATIVE ZOOLOGY. 



Other juitliors liavo devoted eh;ij>tois to " Developiuental Processes," 

 Init none of these ean be eousiderod as at all complete. 



Thus 0. Hertwig, in his "Text-liook of the Embryology of Man and 

 Mammals" (English Translation by E. L. Mark, 189l\ p. 7G), has a 

 "General Discussion of tlio Principles of IVn'elopment." He recog- 

 nized two main ones: (1) the princii)le of uneijual growth (producing 

 folds which are eitlier invaginations or evaginations, and which may unite 

 along their edges) ; and (l!) the principle of histological differentiation. 



Minot, in his Unman Embryology, in a chapter on " Dilferentiation," 

 seems to think also that these two processes are sufficient to explain the 

 ditlerentiation of organs. 



More important in this connection than either of the preceding is the 

 recent paper of Herbst in the " Biologisches Centralblatt " (Vol. XIV. 

 Nos. 18-22). This author, after reviewing the literature upom taxism 

 and tropism, explains as phenomena of the same order certain ontogenetic 

 processes. He has not, however, attem[)ted to catalogue uU the onto- 

 genetic processes. 



Before beginning the present catalogue, T may state that I distinguish 

 between ontogenetic priucip/cs ami ontogenetic processes. Under the 

 first head 1 include such laws of development as terminal growth, repeti- 

 tion of parts and bilateral symmetry in development. These I have not 

 attem[»ted to catalogue. The jtresent paper is concerned only with the 

 latter group, which comprises the ditlerent elementary operations or ac- 

 tions exhibited in ontogeny. 



These niav be divided into two classes : 1. the grosser ontogenetic pro 

 cesses ; and '2. histogenic processes. This paper deals with the first 

 class only. 



In discussing the grosser ontogenetic processes \Ye may distinguish 

 (A) those of a more general nature from (B) the more special ones. 



A. The geueral otitoejenetic processes comprise those of a general physio- 

 logical character. Of these, at least three are commonly recognized : — 



1. Growth (including both the results of assimilation and of inibibitiou 

 of water). 



2. Nuclear division. 



3. Secretion. 



B. The special ontogenetic processes are diflerential in character, i. e. 

 the dilferentiation of the body is eftected by tiiem. 



These jn-ocesses may be classitied. tirst of all, according to the form of 



