ioo DARWINISM TO-DAY. 



schliesst ihre Verneinting in sich, d. h. sie leidet an einem unlosbaren 

 inneren Widerspruch." 



10 This necessity of constantly active selection must apply as well 

 to specialised function as to specialised organ. But it is not diffi- 



Exampleof inef- cult to call attention to certain functions or physio- 

 fective panmixia, logical capacities of various animals which seem to 

 negative this declaration of the need of constant selection to main- 

 tain specialisation. For example, I have shown ("Regeneration in 

 Larval Legs of Silkworms," Jour. Exper, ZooL, Vol. I, pp. 593-599, 

 10 figs., 1904) that the long "domesticated" mulberry silkworm larva 

 possesses the capacity of regenerating any of its legs, if the mutila- 

 tion has not removed the whole appendage. Now the assumption 

 of most selectionists is that this capacity for regenerating injured 

 legs and other parts is a specialisation, adaptive and advantageous. 

 But in connection with this particular case, it should be borne in 

 mind that the silkworm has been for approximately 5,000 years a 

 domesticated animal, cared for under such conditions as to make 

 the natural loss of legs almost an impossible occurrence. Perfectly 

 protected against such natural enemies as bite off legs, there has 

 certainly been nothing of that sharp necessity, during all the life of 

 countless generations of silkworms, which is supposed to be the 

 basis for maintaining the advantageous capacity for regeneration. 

 There has been a clear field for panmixia. But the regenerative 

 capacity still exists in effective degree. 



11 See a recent paper by Vejdovsky ("Uber einige Siisswasser- 

 Amphipoden, III. Die Augenrediiktion bei einem neuen Gam- 

 Example of pro- mar i den aus Irland und iiber Niphargus caspary 



gressive degener- p ratz aus den Brunnen von Munchen," in S. B. Kgl. 



ation not expli- _,... ^ , .... 



cable by natural Bohm. Ges. d. Wiss., 1905), embodying the results of 



selection, his studies on the reduction of the size in certain 



small Crustaceans (Gammaridae), which he found living in the Irish 

 Sea at a depth of from 130 to 150 feet. These Crustaceans form 

 an interesting series showing a gradual reduction of the eyes. It is 

 shown clearly that this reduction proceeds very regularly from the 

 periphery toward the interior. First, there is apparent a high degree 

 of variability of all parts, then the optic parts of the eye disappear, 

 and finally the nervous, or retinal, parts. This course of reduction 

 is only explicable, according to the author, on a basis of the 

 inherited degenerative results of a lack of use, for in any decreas- 

 ing use exactly this course of individual degeneration of the eye 

 is what is met with ; that is, the active external optic elements 

 degenerate first, and later the nervous, or retinal, elements. 



12 Weismann, A., "On Germinal Selection as a Source of Definite 

 Variation," trans. McCormack, pp. 38 ff., 1896. 



