no Herbert Euorene Walter 



and Planaria in 52.5 per cent of the cases. These are differences 

 in degree of response that are great enough to be of unquestion- 

 able significance. When, however, Planaria maculata and Pla- 

 naria gonocephala are compared in the same way, only a slight 

 difference in the degree of response, namely, that between 55 per 

 cent and 50 per cent, is to be observed. 



Manner of Coining to Rest. Although little attention was paid 

 to this point during the series of observations taken up for the 

 present study of planarian behavior, still a few mdications of gen- 

 eric difference in the manner of coming to rest appear from the 

 foregoing data. Bdelloura, it will be remembered, has a distinc- 

 tive manner of coming to rest in close rosettes within an area of 

 increased illumination, while Dendrocoelum shows a considerable 

 tendency to collect in exclusive companies during periods of inac- 

 tivity. With regard to the two species of Planaria studied, nothing 

 at all definite was observed in this connection which could be 

 called a true specific difference in behavior. Between Dendro- 

 coelum and P. gonocephala, however, a decided generic difference 

 seems to exist, as several series of records on orientation in direc- 

 tive light show. Dendrocoelum according to these records came 

 to rest in an unoriented position in 70 per cent of the cases. observed, 

 while P. gonocephala failed to take up an oriented resting position 

 in only 59 per cent of the observations. In other words, P. gono- 

 cephala is more liable to come to rest in a position oriented with 

 reference to the light than Dendrocoelum. 



Summary. The essential points brought out in the foregoing 

 section are condensed for the sake of brevity and clearness in 

 Table XXV. 



In certain instances, namely, in changes in the character of the 

 course (2), the influence of fatigue (yj, and the percentage of 

 responses to change in light intensity (8), specific behavior shows 

 a more intimate correlation than generic behavior, otherwise the 

 range between the behavior of P. gonocephala and P. maculata is 

 greater than the generic differences separating Planaria from the 

 other genera under observation. 



It might be expected a prion that generic differences would 

 exhibit a greater range than specific differences and that similarly, 



