l68 C. M. CHILD. 



and various other factors. In shorter individuals, for example, a 

 relatively larger fraction, though an absolutely shorter piece, is 

 necessary for a certain result similar to that produced by a rela- 

 tively smaller fraction, though absolutely longer piece from a 

 longer individual. Moreover, even in the same individual paired 

 eyes appear in pieces of a certain length from the anterior region 

 and the region of the second zooid, while pieces of the same 

 length from the middle region produce either single eyes or else 

 remain headless. With continued starvation the length of a piece 

 necessary to produce a given result as regards eyes increases. 



With this brief statement of the results of experiments in water 

 we may now turn to the consideration of the anaesthetics. In the 

 anaesthetics single eyes appear in much longer pieces than in 

 water. By preparing similar pieces of the proper length from a 

 certain region of the body and placing part of them in alcohol, 

 or ether, part in water, it is often possible to obtain lOO per cent, 

 of single eyes in the anaesthetic medium and lOO per cent, of 

 normal paired eyes in the water. 



But in the anaesthetic a rather remarkable further change 

 occurs very frequently, though I have never observed it with 

 certainty in water. After some two weeks or more in the anaes- 

 thetic the single-eyed heads give rise to two additional eyes 

 symmetrically placed in the normal position and slightly posterior 

 to the single median eye already present. These three-eyed in- 

 dividuals are a characteristic feature of the experiments with 

 anaesthetics. All the eye-spots persist as long as the animals 

 live, whether they remain in the anaesthetic or are returned to 

 water. 



But still another feature must be noted. The longer pieces in 

 the anaesthetic frequently produce two eyes in the normal posi- 

 tion. In many cases such pieces give rise after two weeks or 

 more to a second pair of eye -spots a short distance behind the 

 first pair and, like them, symmetrically placed. Such individuals 

 then possess four eye-spots, all of which persist during life. 



Briefly then a very common effect of the anaesthetic is to in- 

 crease the number of the eye-spots beyond the normal. It 

 should perhaps be noted that these additional eye-spots are not 

 mere fragments of pigment, but typical eyes, the pigment being 



