The Role of the Chromosomes 227 



are pigmented also. If the young of specimens living in the 

 open are kept in the dark during development, the pigment is 

 more or less absent. Different species of salamanders show 

 differing results when reared in artificial caves ; in some there 

 is very slight reduction of pigment and in others this reduc- 

 tion is temporarily almost complete. These latter however 

 may develop the normal amount of pigment at metamorphosis. 

 Vice versa, cave animals lacking pigment may or may not 

 develop pigment, when reared in the light. Possibly the less 

 responsive types are those which have lived longest in their 

 respective habitats. However the fact that there is consider- 

 able individual variation in this respect suggests that some 

 other factor is involved. 



An interesting adaptation of certain cave animals is their 

 greater sensitiveness to tactile than to light stimuli as com- 

 pared with their free-living relatives. 



Animals respond readily to chemical treatment. Some of 

 the most noted experiments along this line are those of 

 Stockard in the production of Cyclopean fish. By treating 

 developing minnows with magnesium salts, alcohol, chloro- 

 form, etc., he has replaced the paired eyes with an unpaired 

 median one resembling that of the fabled Cyclops, and similar 

 results have been obtained by McClendon and Werber. Not 

 only may Cyclopean monsters be formed by chemical treat- 

 ment, but deformities of many kinds. Eye deformities may 

 range all the way from various stages in the approach and 

 fusion of the eyes, through Cyclopean eyes, to no eyes at all. 

 The eyes may be rudimentary in size and displaced dorsally ; 

 or there may be inequality of the two eyes, leading to the 

 absence of one of them. An eye may even be developed 

 entirely outside the body of the embryo, on the surface of 

 the yolk sack. Abnormalities of the eyes are usually accom- 

 panied by those of nose and mouth, which are frequently 

 drawn out into a snout-like projection. In cases in which one 

 eye is lacking its place may occasionally be taken by the 

 mouth. The nasal pits may fuse into one, and the same 

 may be true of the ears. Or these latter may be enormously 

 swollen, or on the contrary exceedingly small, when one or 

 more of the semi-circular canals may be defective or lacking. 

 Partial embryos may occur, or the parts of the embryo may 

 develop separately, as in the case of a yolk sack eye, already 

 mentioned. In fact every imaginable deformity may be pro- 

 duced by chemical treatment, from very slight defects to those 

 so great that the resulting creature is merely a formless 

 mass of living matter. 



Abnormal development may sometimes run a more orderly 

 course and produce symmetrical, relatively perfect creatures 



