Januaky 22, 1904.] 



SCIENCE 



141 



nifieanee of the multiform colors more or 

 less general among members of the coelen- 

 tera? It seems to me more or less evident 

 that natural selection can have at best but 

 ■a limited place in its explanation. I see 

 no place for it along the lines of pi-otec- 

 tion, either direct or indirect. 



Of even less significance can any modi- 

 fication of it under the guise of sexual se- 

 lection be claimed ; for even aside from the 

 large majority of cases where there is 

 slight if any sex differentiation, no sen- 

 sory organization, which Darwin recog- 

 nized as essential to the exercise of this 

 factor, is present through which it might 

 become operative in even the smallest 

 degree. 



Two, and only two, other methods of 

 explanation have seemed to me to afford a 

 reasonable account. First, that it is due 

 primarily to the normal course of metabo- 

 lism, during which color appears as one 

 of its many expressions. Darwin himself 

 was not indifferent to this possibility, and 

 expressly states in connection with the 

 same problem that color might very nat- 

 urally arise under such conditions. ' ' Bear- 

 ing in mind," he suggests, "how many 

 substances closely analogous to organic 

 compounds have been recently formed by 

 chemists, and which exhibit the most splen- 

 did colors, it would have been a strange 

 fact if substances similarly colored had 

 not often originated, independently of any 

 useful end thus gained, in the complex 

 laboratory of the living organism." It 

 has also been pointed out in an earlier 

 portion of this paper that Wallace had 

 to appeal to a similar source in his search 

 for the primary factors of animal colora- 

 tion. 



Geddes and Thomson in discussing the 

 problems of sex likewise make a similar 

 claim. They declare, "pigments of rich- 

 ness and variety in related series, point to 



preeminent activity of chemical processes 

 in the animals which possess them. Tech- 

 nically expressed, abundant pigments are 

 expi'essions of intense metabolism." They 

 further find in the phenomena of bright 

 colors among the males of most of the 

 higher animals simply the expression of 

 the correspondingly greater activities of 

 the process of metabolism. 



I believe that in this source we have a 

 real account of a considerable body of color 

 phenomena among the lower invertebrates, 

 and particularly of that series under pres- 

 ent consideration. 



The second factor to which I would ap- 

 peal is so nearly related to the former as to 

 be involved more or less intimately there- 

 with. It is to the effect that certain pig- 

 ments are products of waste in process of 

 elimination. This has already been re- 

 ferred to in a former connection and need 

 not be separately emphasized apart from 

 the concrete cases to which it may be 

 applied. 



Strongly significant of the importance 

 of this process among the Hydrozoa is the 

 fact already pointed out that pigments are 

 found deposited along the lines of prin- 

 cipal metabolism, namely, the gastrovascu- 

 lar regions, the gonads, and to a less extent 

 the immediate regions of sensory bodies, 

 when these may be present. While this 

 alone as a mere statement of fact does not 

 prove the point at issue, when taken in con- 

 nection with other facts of a similar na- 

 ture, it amounts to a high degree of prob- 

 ability. 



What evidence have we that in the ease 

 of hydroids, medusse, etc., colors are asso- 

 ciated with excretory .processes? While 

 the facts are not numerous, they are, I 

 believe, rather convincing. In work upon 

 regeneration in hydroids, Driesch and 

 Loeb called attention to certain pigmen- 

 tary matters found in Tuiularia and 



