152 ROBERT BENNETT BEAN 



The hypo- and hyper- are both undergoing retrograde meta- 

 morphosis, the hyper- in America, the hypo- in Asia, and the 

 Meso form carries the evolution for the future. 



It is noted that the Fihpinos are more precocious than the 

 Americans in the eruption of the permanent teeth, although the 

 Filipinos are more hypo- than the Americans, and the hypo- is 

 more backward than the hyper- in this respect. Therefore the 

 precocity of the Filipinos must be attributed to something other 

 than hypermorphism. Whether it is race, climate, food, water, 

 animal parasites, or something else, is problematic. 



PHYSIOLOCilCAL STANDARD 



Each tooth may be considered from the standpoint of the time 

 at which it first appears in any individual, and the time at which it 

 last appears in any individual, as well as from the time at which 

 50 per cent of the individuals have the tooth erupted, and the time 

 during which the greatest number of individuals have the tooth 

 erupting. Suppose we take the left upper second molar tooth 

 in the American girls. This tooth has not erupted in any Ameri- 

 can girl at 9 years of age, but 2 per cent appear at 10 years, and 

 the latest age at which any erupt is 15 years, all are erupted at 

 16 years. Approximately 50 per cent have the tooth erupted at 

 12 years, therefore there is a shorter period for the eruption 

 of the first 50 per cent (10 to 12 years), than for the eruption of 

 the second 50 per cent (12 to 15 years). The greatest number 

 of teeth erupt between 1 1 and 12 years (41 per cent) although there 

 is a second period of rapid eruption between 13 and 14 years. 

 Thi.s may be a segregation of the precocious and backward Ameri- 

 can girls. 



In like manner we may obtain the same data for all the other 

 teeth of the American girls, and of the teeth of all the other boys 

 and girls. The upper teeth of the same type on the two sides, as 

 the upper median incisors, erupt at so nearly the same time that 

 they may be put together. The periods of most rapid eruption 

 almost invariably coincides with the time at which 50 per cent of 

 the teeth have erupted therefore the limits of the first mentioned 

 period will cover the second. Table 1 (p. 155) has been constructed 

 showing the results, and this table will be the physiological stand- 



