PISCES 161 



the result is a series of monsters, ranging from those in which only the 

 most anterior structures (nostrils and eyes) are abnormal to blind and 

 nearly headless forms. Between these extremes are types in which the 

 eyes are too close together and the mouth narrow and protruding; 

 those in which the eyes are fused into a single median cyclopian eye 

 and the mouth is a sort of extended proboscis; and those in which the 

 merest rudiments of eyes or other anterior structures are developed. 

 All of these types are to be interpreted, according to the nomenclature 

 of Child, as the results of differential inhibition; which implies that 

 the parts of the body that normally have the highest rate of metab- 

 olism and are the first to differentiate, are the parts that are most 

 readily inhibited by growth-depressing agents; while the parts that 

 have the lower or lowest metabolic rates are least affected by the 

 same agents. 



How then can we explain the type in which the posterior parts are 

 relatively inhibited, and the anterior parts, together with the apical 

 parts of the secondary and tertiary axes, are relatively more highly 

 differentiated? These conditions become instantly intelligible as the 

 result of another type of experiment with Fundulus eggs and em- 

 bryos. If eggs are placed in a weak solution of alcohol or cyanide and 

 are allowed to remain there indefinitely, the rate of metabolism, and 

 consequently of development, is generally retarded for a time, but 

 gradually a process of acclimation or recovery takes place, the result 

 of which, curiously enough, is that the parts that primarily were most 

 seriously inhibited are the first to become acclimated, and recover 

 more completely than the other parts. If the solution be made strong 

 enough to be lethal for most of the embryos, a few of the hardiest of 

 them undergo a very Umited recovery, involving only the most apical 

 structures, such as eyes. Several investigators have obtained, in 

 ways similar to that described, embryos that consisted of nothing but 

 isolated eyes; and it is very common to find, as the result of less ex- 

 treme measures, embryos that consist merely of heads with large 

 roUing eyes and provided with a tiny undifferentiated appendage that 

 stands for the rest of the body. Other embryos that are mainly heads 

 develop in addition large wing-like pectoral fins; still others become 

 bro'ad and flat, like a Skate, or high and compressed like a Head-Fish. 

 In fact a good assortment of experimental monster fish embryos will 

 furnish parallels to most of the stock types of form distortion seen 

 in the specialized and degenerate groups of fishes. Of course none of 



