86 'Journal of Comparative Neurology and Psychology. 



Reaction to Tactile Stimuli. 



A. Response to Stimulalion on the Head. 



According to their reaction to a touch on the side of the head, 

 in the region innervated by n. trigeminus or n. vagus, embryos of 

 Diemyctylus torosus may be grouped according to three types, as 

 follows : 



Type I. Embryos which from the beginning and during a consid- 

 erable period, respond regularly or almost regularly with a move- 

 ment of the head directed away from the side touched. 



Type II. Embryos which for a relatively short period at first 

 respond irngularly with movements of the head toward or away 

 from the side touched, and then enter upon a relatively long period 

 of response like that of Type I. 



Type III. Embryos which are at first asymmetrical in response, 

 that is to say, they move their head in one direction only, regardless 

 of the side touched, and then enter ujxm a short period of irregu- 

 larity like the first period of Type II, and finally upon a relatively 

 long period of response like that of Type I. Or individuals of 

 this type may pass directly from the period of asymmetry to the 

 regular form of Type T. The accompanying charts illustrate the 

 behavior of typical specimens from each of these three types. The 

 first column on the left in these charts records the serial number of 

 the trials made, and the record of each trial is represented in the 

 corresponding horizontal line to the right. The figures in the second 

 column from the left record the time in hours and minutes that 

 elapsed since the last ])reccding trial in each case. The diagrams in 

 the third column from the left represent the form of reaction in the 

 various trials. ^^Tlere there is more than one diagram in a space 

 these are to be read from left to right, and each represents a distinct 

 phase in a series of movements. The arrow occasionally placed in 

 these spaces indicates that a cephalo^caudal progression of the move- 

 ment w\as distinctly observed. Where an ^'S" occurs the specimen 

 swam, and the following diagram in the same space indicates the 

 composition of the swimming movement. It should be noted that 

 these diagrams of the movements are simply free-hand representa- 



