46 INHERITANCE IN SILKWORMS, I 



functionally degenerate organ. The material consists of the wings of 

 52* individuals derived from larvae which had been subjected to various 

 conditions of feeding as follows : 



(Lot 399, sub. i.) Moths from larvae fed optimum amount of 

 food during entire experimental history. 



(Lot 399, sub. 2.) Moths from larvae given short rations during 

 a single (the immediate) generation. 



(Lot 399, sub. 3.) Moths from larvae given short rations for one 

 year, optimum for the following (the immediate) generation. 



(Lot 399, sub. 4.) Moths from larvae given short rations during 

 past two generations. 



It was thought that upon seriation of the data there might be 

 found some correlation between the variations and the conditions of 

 feeding within each sub-lot. It was realized, however, upon seriation 

 of the data, that while there are certain unique and suggestive varia- 

 tions in certain sub-lots, the series is numerically too short to justify 

 any correlation of variations with conditions of nutrition. Therefore 

 in the following tabulation of results, the variations are seriated for 

 the 52 individuals as a whole, the interest centering in the degenerating 

 structural condition of the venation in this organ which is functionally 

 degenerate through disuse. 



Many of the 104 wings exhibit numerous variations from the 

 typical venation (Fig. i) of the species. These variations may be 

 classified in three groups as follows : 



1. Variation by addition of spurs or of short veins to the typical 

 venation. 



2. Variation by loss of certain veins in full or in part. 



3. Variation by loss of veins proper, i. e., the absence of chitiniza- 

 tion combined with the persistence of tracheae which are disposed : 



(a) in such a position as to take the place of veins belonging to 

 the typical venation of today ; 



(b) along ancient lines of development, as where the extinct base 

 of media is preserved intact in the discal cell. 



i. Variations by addition. 



The variations classified under this heading are very few numerically 

 and very insignificant in kind, adding but a fractional amount to the 

 total extent of the wing's venation. 



* In the 52 pairs of wings some were broken in certain areas so that every study does 

 not include the entire 52 pairs. 



