Vol. 11 Bovard. — Senst Organs in Microscolex Elegans. 279 



organs immediately about the opening does in Lumbricus. Sec 



oiiilly, in the burrow or on a rough surfi the side to side 



motion, so characteristic of the worms, would make the sides 

 also a region of first contact with the environment, consequently 

 we might expect the body to be sensitive here and to have more 

 sense organs. The ventral surface is seldom off of the sub- 

 stratum, first, because a better hold is gained here with the 

 chaetae; and second, because gravity tends to keep that side 

 in contact with the earth. For these reasons the ventral surface 

 would have more use for sense organs than the dorsal, whose 

 surface would he stimulated only by occasional rather than by 

 constant contact. 



The distribution of the sense organs suggests that Hie surface 

 of the worm is not equally sensitive in all parts. Experiments 

 to determine the sensitiveness were made, with alcohol and acids 

 as irritants, sugar and quinine as taste stimulants. A fine 

 capillary pipette was used for applying alcoholic solutions of 

 1 per cent, and less, so that a small quantity could be applied 

 to a small area. The time between the application and some 

 direct manifestation of irritation was recorded by a stop watch. 

 The records show' that the anterior end is more sensitive than 

 the posterior, and the posterior more than the middle part. 

 Solutions of quinine of one thousandth of 1 per cent, and 

 even less gave the same results as the alcohol. The fact that 

 the animals reacted to the quinine may indicate that the sense 

 organs have some gustatory function. This might be expected, 

 for the difference in structure between sense organs on the out- 

 side of the body and those of the pharynx is very slight. The 

 sense organs of the pharynx are lower and a great deal broader 

 than the others. The results of the last set of experiments are 

 of importance because they show that the degree of sensitiveness 

 inferred from the differences in time reactions of a given region 

 is correlated with the number of sense organs found therein. 

 The ratio of the number of organs in the anterior end to those 

 of the posterior is 3 : 2, while the ratio of time reactions is 

 approximately 4 : 7. Thus the ratio of the numbers of sense 

 organs in two given areas is approximately inversely propor- 

 tional to that of the time reactions. This relation is shown in 



