OF ARTS AND SCIENCES. 17 



ment cells, would naturally transmit to their progeny in the greatest 

 quantity only such pigment as would most easily reproduce the imita- 

 tion of sand, while the same might be true of the Flounders living 

 on muddy or gravelly bottoms. Something analogous exists in the 

 common Echini, where dark-green and violet pigment spots closely 

 imitate dark granitic rocks covered with seaweeds ; or in the imitation 

 of sand by the grayish-green tint of Mellita and the yellow tint of Am- 

 phidetus, &c. : yet the whole theory of mimicry, even in these cases, 

 as a means of protection, is again overthrown by the mass of Clypeas- 

 troids, Spatangoids, Echinoids, whose dark coloring, but for their habit 

 of burrowing in the sand in which they live, would make them most 

 prominent objects. We next have the legions of Ctenophorse, Jelly 

 Fishes,' and of other pelagic animals (especially the embryos) so trans- 

 parent as to be scarcely distinguishable from the water in which they 

 live, many of them are reduced to the merest film. Have they all, 

 little by little, assumed their transparency, in order to escape their 

 enemies ? Then why do they swarm in such quantities that their numbers 

 counteract the very object of their transparency ? It is common along 

 the seashore, at proper times of tide and wind, to find long lines where 

 all these delicate and transparent animals are accumulated on purpose as 

 it were to provide the food needed by their enemies, who are at hand 

 playing sad havoc among them. Many of the embryos of our com- 

 mon marine animals are gregarious for a short period of their life ; for 

 instance, the young of the majority of our Crabs and Shrimps, of many 

 Gasteropods, Annellids, and Radiates, just at the time when they are 

 mosf delicate, and least capable of escaping the attacks of their enemies. 

 At the time of hatching of the young Prawns {Palcemonetes vulgaris), 

 and of the young of our Cancer, sea perch may be seen devouring them 

 by the wholesale while they are swarming close to the shore. Thus, 

 numberless young are destroyed in spite of their transparency, and the 

 same holds good for a host of other embryos. 



In the Flounders, we seem to have fair evidence that they are able 

 to produce certain effects in consequence of impressions received upon 

 the retina, and that the changes taking place on the chromatic side of 

 the body are probably due to the capacity of the fish to distinguish cer- 

 tain colors from others. But more accurate experiments than I have 

 yet made are necessary to enable us to decide whether the sense of 

 color is developed so early in the Vertebrate series, or whether we have 

 simply a set of reflex actions. It certainly seems, from a physiological 

 point of view, very hazardous to infer — as has been frequently done 

 on philological grounds — the gradual development of the sense of 



VOL. XIV. (n. S. VI.) 2 



