1S96.J ol [Conklin. 



conclusion that the whole course of developmental phenomena must be 

 referred to organization of some sort. Development, no less than other 

 vital phenomena, is a function of organization." 



3. A study of the phenomena of development, as well as the prin- 

 ciple of causality, make it certain that all the characters of the species 

 are predetermined within the protoplasm of the fertilized egg cell. 

 From a frog's egg only a frog will develop, from an echinoderm egg 

 only an echinoderm, and the course of the development is, under 

 normal circumstances, definitely marked out in each case, even down 

 to the minutest details. All the results of experiment, as well as 

 observation and induction, only serve to render this conclusion the 

 more certain. It should be observed that to affirm that characters are 

 pi'edetermined is a very different thing from saying they are preformed. 

 The one merely asserts that the cause of the transformations which 

 lead from one step to another in the development is determined by the 

 initial conditions of the fertilized egg cell ; the other affirms that those 

 transformations have already taken place. 



The absolute determinism of development depends primarily upon 

 the constant structure of the egg cell, but also to a certain extent upon 

 a definite relation to extrinsic factors. Since, however, these extrinsic 

 factors may be exactly the same in two cases, and yet the result of de- 

 velopment be very different (e, g., the egg of the starfish and that of 

 the sea urchin), we can only conclude that while ontogenetic difi'erences 

 may be caused by a disturbance of the extrinsic factors, inherited char- 

 acters are always the result of a definite structure of the germinal pro- 

 toplasm, and that, therefore, development is, in the words of Prof. 

 Whitman, "a function of organization." 



Inheritance and variation are general terms which include a great 

 many different kinds of phenomena, many of which seem to be due to 

 entirely different factors. A great many phenomena of inheritance 

 seem to be due entirely to extrinsic forces, but a more careful inquiry 

 always reveals the fact that they are invariably due to the reaction of 

 certain extrinsic causes on a perfectly definite living structure. As 

 examples may be mentioned the following : 



(1) The tiger-like striping of the egg of Fundulus, which is very 

 characteristic and would certainly be regarded as an inherited char- 

 acter, has been shown by Loeb* to be due entirelj' to the position of 

 the blood vessels of the blastoderm. The pigment cells are at first 

 uniformly distributed, but when the blood vessels are formed they 

 gather around them, probably through chemotropic action, and thus 

 the characteristic banded appearance is produced. Graf has since 

 shown that the color paterns of leaches are produced in the same way. 

 It is not necessary, therefore, to assume that the color paterns in these 

 cases are specifically represented in the germinal protoplasm ; it maj^ 



* Jacques Loeb, Some Facts and Principles of Plnjsiological Morphology, Biological Lec- 

 tures, 1893. 



PhOC. AMEIi. PHILOS. SOC. XXXV. 150. K. PRINTED JULY 7, 1896. 



