2 34 ' BIOLOGICAL LECTURES. 



"laws" maintains that every marking is at first longitudinal. 

 The truth of the matter is that most animals are not spherical, 

 and that most organs, especially in segmented animals, run in 

 a lono-itudinal direction through the animal ; for instance, the 

 spinal cord, vertebral column, blood vessels, intestine, etc. In 

 the embryo it is especially true for the large blood vessels. 

 The first striation in such embryos is, of course, longitudinal, 

 simply because it is determined by the blood vessels ; but wher- 

 ever we have to deal with the coloration in a spherical organ, 

 as, for instance, in the yolk sac of the Fundulus embryo, the 

 absurdity of Eimer's law becomes evident. Here, on the sur- 

 face of the sphere, there is no longitudinal direction, and yet 

 here, too, the chromatophores follow the blood vessels. In 

 the same way the so-called law of Eimer appears absurd if we 

 consider the marking, which is determined by the pigment cells 

 that cover the brain. 



Although it seems to me that at present we cannot avoid 

 dealing with the problem of heredity from an analytical point 

 of view, it is clear that this is only a temporary necessity. 

 Sooner or later the facts found by the analytical method must 

 be utilized for the establishment of more general laws. 



