140 



SCIENCE. 



[N. S. Vol. XIX. No. 473. 



cies. Duerden lias called attention to this 

 feature among both corals and actinians, 

 and believes it to be due to the presence or 

 absence of greater or less intensity of light, 

 and believes it to be an expression of the 

 fact that the Zooxanthellse are not able to 

 thrive except under proper light, and that, 

 moreover, where light is too intense, as in 

 shallower waters, certain dark pigment 

 foiind in such specimens is thought to be 

 due to its utility as a screen. "While there 

 may be a measure of credibility as to 

 phases of this view, it does not seem to me 

 as of general adequacy. The variability 

 of species to which I have just referred 

 and to the very common genus Metridium 

 is certainly not due in any appreciable de- 

 gree to the factor of light, since it occurs 

 indiscriminately among specimens taken 

 in identical situations as well as under 

 those of differing conditions. 



In this connection may be mentioned the 

 same phenomenon among medusae. The 

 variation of coloration in Cyanea has long 

 been known and is so marked that the 

 elder Agassiz distinguished two additional 

 species chiefly on this character, both of 

 which have long since been discarded. It 

 is quite well known to observers that these 

 animals when placed in aquaria usually 

 show within a very short time a more or 

 less marked diminution in colors. Dacty- 

 lometra, while living fairly well for many 

 days in the aquarium, loses within this 

 time so much of its usually bright colora- 

 tion as not to seem like the same creature. 

 The same is true of many other animals 

 than medusa". On the other hand, it is 

 equally well known that many other ani- 

 mals may be placed under these more or 

 less artificial environments with little ap- 

 parent loss in this or other respect. That 

 it is not due to light alone is evident in the 

 fact that similar changes occur in medusse 

 which have been kept in open pools or 

 enclosures about docks or elsewhere. 



It seems to me rather that the true ex- 

 planation is to be found in the changed 

 conditions of nutrition and the consequent 

 change in the metabolism of the animal. 

 Hydroids placed under these conditions 

 show the same tendency. 



Those which take kindly to the change 

 show no appreciable decline as to color or 

 other vital process. The same is true of 

 medusas. Gonionemus may be kept for 

 weeks in the aquarium, and if properly fed 

 will show no decline in color, while if the 

 conditions become bad an immediate 

 change is noticeable in this as well as other 

 features. 



The same may be said concerning the 

 actinians. While many seem to suffer no- 

 ticeably when placed in aquaria others 

 show no apparent difference. Gerianthus 

 membranaceus, one of the finest of the 

 actinians to be seen in the Naples aqua- 

 rium, and one of the most variable, shows 

 no apparent decline in any vital function. 

 Specimens have been kept in flourishing 

 condition in the aquarium for several 

 years and show no sign of decline, the col- 

 oration continuing as brilliant as in the 

 open sea. The same is true of many other 

 organisms found in finest condition in this 

 celebrated aquarium. Among the annelids 

 Protula soon shows decline in color vigor, 

 and the same is true, though to a less 

 degree, in the case of Spirographis and 

 Ser^nila. 



While it may not be without probability 

 that some measure of this color change 

 may be due in certain cases to the changed 

 conditions of light, it still remains true, 

 I believe, that light alone is but a single 

 factor, and that often a minor one involved 

 in the changes observed, and that changed 

 conditions of nutrition and metabolism are 

 by far the more important. 



The main factor of our problem, how- 

 ever, is still Tinsolved. What answer shall 

 we make to ourselves concerning the sig- 



