RESULTS 307 



Average. 



For 20 Hamilton specimens 111.9 



21 Ithaca zone specimens 108.1 



115 Van Etten specimens 109.3 



40 Owego speciiiiens 105.6 



79 Swartwood specimens 108.2 



Extremes of 

 fluctuation. 



Amount of 

 fluctuation. 



104.5-118.2 



13 7 



99.2-125.5 



26.3 



73.4-147.8 



74.4 



91.0-119.5 



28.5 



91.3-137.3 



46.0 



Average for the whole set 108.2 



From these statistics it is evident that the amount of ph3dogenic modi- 

 fication of this character E^ (105.6 to 111. 9 = 6. 3 per cent) is extreme!}' 

 small in comparison with the ontogenic fluctuation (see last column in 

 above table) for any one of the zones examined.^ 



Amowit of ontogenic fluctuation great. — The amount of the ontogenic 

 fluctuation is brought to light in another way by tabulating the differ- 

 ences^in value of the index R^ for each separate sample lot and computing 

 the average for the whole 35 lots. 



There are 35 lots of specimens, each lot from a single localit}^ and 

 faunule. The range of fluctuation in value of the index R^ for each lot 

 is shown by the following summary : 



7 lots show no variation, because there is but a single specimen in 



evidence 



6 lots show a range of fluctuation less than 10 per cent 



6 lots show a range of fluctuation between 10 and 19 



11 lots show a range of fluctuation between 20 and 29 



1 lot shows a range of fluctuation between 30 and 39 



3 lots show a range of fluctuation between 40 and 49 



1 lot shows a range of fluctuation of 58 



The average amount of fluctuation in value of R^ for the 35 lots is. . 17 



The fluctuation of this character expressed by the type figures of 

 several described species is as follows: 



Amount of fluctuation. Mean. 



OvtMs cydas Hall 110.8-117.1 = 6.3 per cent 113.9 



Orthis idoneus 107 - 113.8= 68 per cent 110.4 



Orthis leucosia 103.5 - 112 = 8 5 per cent 107.7 



Orthis penelope 106.7 - 121 = 14.3 per cent 113.8 



Orthis vanuxemi 107 -111.8= 4.8percent 109.4 



and the total difference in form expressed in values of R^ for tbese five 

 Hamilton species, as above enumerated, based on measurement of the 



' Phylogenic modification is the amount of morphologic change distinguishing the rep- 

 resentatives of one stage from tliose of another following stage of its history ; ontogenic 

 fluctuation is the change in form expressed by different individuals of the same race 

 living at one and the same time. 



