262 J. S. NICHOLAS 



EXPERIMENTS ON LARVAE 



Four series of larvae were kept under observation, namely, 

 1) eyeless, those animals in which the optic vesicles had been 

 removed; 2) noseless, those which had been deprived of the nasal 

 placodes; 3) eyeless and noseless, those from which both the optic 

 vesicle and the nasal placodes had been removed; 4) a series of 

 normal animals which served as controls and were of considerable 

 use in a comparative study. 



Under practically the same conditions, it could be easily seen 

 that the normal larvae soon outdistanced the operated in growth. 

 The noseless animals were slightly smaller than the normals of 

 the same age. Next in size were the eyeless forms, and finally 

 the eyeless and noseless, which were considerably smaller than 

 the eyeless. 



In a general way, the rate of growth shows the relative im- 

 portance of the senses of sight and smell. The sense of sight 

 is of more use in the obtaining of food at this stage than is that of 

 smell. If the conditions of the amount of food present are varied, 

 however, there is a change in the relative importance of the 

 senses, for when food is scarce the sense of smell seems to domi- 

 nate. This is shown in the following observation. The noseless 

 forms seem to have no ability for distinguishing whether a 

 particle is a food substance unless that particle has motion. 

 The eyeless forms have a distinct advantage in this connection 

 for they will distinguish pieces of organic material. If pieces 

 of dead earthworm are placed in an aquarium, the noseless animals 

 will push them around as they do other bits of debris, but will 

 seldom snap at them. The eyeless, in direct contrast to this, 

 will devour the earthworm immediately after coming in contact 

 with it. 



A marked difference was noted in the responses to rapidly 

 diffusing food substances obtained in the different groups of the 

 larvae. When freshly cut earthworms are placed in the aquaria, 

 the normal animals begin to swim rapidly about without making 

 any attempt to locate the stimulus. They will often snap as they 

 pass through the area occupied by the diffusing substances. 



