94 'Journal of Comparative Neurology and Psychology. 



noted that the figures in Column B represent the maximum possible 

 time of irritability before the observation of it began. On the other 

 hand, a comparison of the averages in Cohunn G shows a clear dis- 

 tinction between Type I, on the one hand, and Types II and III, 

 on the other. There is a difference of, say, 10 to 15 hours in the 

 length of the period of regularity in moving the head away from the 

 side touched. Furthermore, if the average of Column G for Type 

 I be compared with the corresponding average for Type II plus the 

 averages of Column E and F of this type, it will be seen that the 

 embryos of Type I were longer in passing throngh the one period 

 of regularity than were the embryos of Type II in passing through 

 the periods of both regularity and irregularity, including the inter- 

 val. It would seem, therefore, that a period of irregularity has 

 not been passed over unobserved in Type I, and that the distinction 

 between these two types is not based on the relative age of the indi- 

 viduals when they came under observations. 



A similar comparison of the corresponding figures for Type III 

 with those of Type I shows that the time represented by Columns 

 E, E and G for Type III approximately equal that of Column G 

 for Type I, But for the excessively long period of ISTo. 38 in 

 Column G, the comparison would result about the same as that with 

 Type II. But when the period of asymmetry and the following in- 

 terval is taken into account it is clear that the specimens of Type 

 III were a much longer time in passing through the periods repre- 

 sented by Columns C, D, E, F and G than were the specimens of 

 Type I in passing through the period of Column G alone. This 

 would seem to indicate that the condition of asymmetry is due to a 

 precocious development of one side of the neuro-muscular svstem 

 rather than to a retarded development of the other side. At any 

 rate the sum of the averages in Columns C and D for Type III is 

 greater than the average in Column B for Type II. It would seem 

 altogether improbable, therefore, that a period of asymmetiy like 

 that of Type III has been passed over unobserved in Type II. 



^Miile I do not place any great dependence upon this comparison 

 of the averages in the table, I believe they do tend to show that the 

 difference between the different types of reaction as observed in these 



