OF ARTS AND SCIENCES. 13 



that of the organs of sense of the embryos. "We might add here, 

 in favor of this view, the asymmetricals of many Acalephs (Hyboco- 

 don), in which the disproportion of one of the organs of sense (tenta- 

 cles) is very great. He further calls attention to the faets that, in 

 Pteropods, it is the organs of sense which first show asymmetry, and 

 suggests that cyclopism has been an indirect cause of restoration of 

 symmetry; though this point does not seem well taken, — judging, at 

 least, by what we know of the development of cyclopism among 

 Crustacea. At any rate, the action of light upon organs of sense, 

 which in all embryos are developed out of all proportion to their ulti- 

 mate conditions, must remain an all-important element in its effect 

 upon the nervous system. In embryos so transparent as many young 

 fishes, which seem to be nothing but eyes, brain, and notochord, the 

 action of light must be infinitely more potent upon the nervous system 

 than it can possibly be in older stages, when the muscular system has 

 obtained a so much greater preponderance. The sensitiveness of young 

 fishes to the slightest disturbance of the water, either as a shock or 

 from light, is exceedingly acute ; while, when older, they are appar- 

 ently insensible to the same causes. 



I have nothing to add to the explanation of the mechanism of color- 

 ation given by Pouchet in his admirable memoir on the change of 

 coloration, to which I have already referred. A recapitulation of the 

 important points may, however, help the reader not familiar with his 

 memoir to understand the changes taking place during the develop- 

 ment of our young Flounders. In the coloration of fishes, we must 

 distinguish colors due to interference of light produced by the presence 

 of thin plates, and those due to anatomical elements frequently highly 

 colored, and endowed with sarcodic movements capable of marked 

 changes of form, under special influences, so as to present the shape 

 of extended dendritic surfaces or minute spherical masses through 

 which the pigment is distributed. The changes of coloration due to 

 thin plates are, of course, exceedingly variable, the tints following each 

 other with great rapidity, according to the angle at which we view them. 

 Such lamellar coloration is common among insects, Crustacea, and also 

 in some families of fishes. Among the most beautiful examples are those 

 of the dolphin ( Goryphcena) and of Saphirina ; while the second class 

 of colors — those due to the movements of the anatomical elements — 

 are directly connected with the impressions of color received by the eye, 

 and brought about by the reflex action of the nervous system. That 

 this is the case, the rapid change of coloration produced by placing 

 Flounders upon differently colored bottoms sufficiently proves. This 



