222 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



flattened and disintegrated, that is, crossed by sutures running in dif- 

 ferent directions which permit them to bend lengthwise as well as 

 transversally ; in the nonthanatotic Cleptinae the urosterna are undi- 

 vided and a little convex. 



The lack of more thorough knowledge on the ethology of these 

 Hymenoptera does not permit me to discuss objectively what I had 

 formerly learned. However, it may be observed that : ( i ) in regard 

 to the thanatosis of the Chrysidinae, the disintegration of the 2d to 4th 

 urosterna permits a very intimate mutual adaptation between f orebody 

 and lower surface of the gaster (obviously this does not correspond to 

 a necessity, nor is it of use in rolling up) ; (2) with regard to the 

 solenogastria, the ability to lengthen telescopically the urites nearer 

 to the hind end of the gaster is clearly correlated with oviposition 

 within closed cells or cocoons, but even here it is not at all a necessary 

 condition, because the point to be reached may be attained without a 

 gaster of this type, as is shown by the pseudosolenogastric Chrysididae. 



CONCLUSIONS 



Data could be multiplied and collected from different fields, but 

 from what has been summarized above and from the coordination of 

 the observations described, it is possible to come to the conclusions 

 here summed up in 18 units. 



1. The modifications undergone by the organisms studied by me 

 (insects of several families belonging to three orders of Holome- 

 tabola in both imaginal and preimaginal stages) are always connected 

 with the function which the organ or the group of organs concerned 

 has to perform, and on the whole with the work the organism has 

 to do in the particular environment in which it lives. 



2. These modifications can be collected into about five classes : 

 (A) involutions, rudimentations, or disappearance of organs or por- 

 tions of organs; (B) abnormal (hypertelic) developments of organs 

 or portions of organs; (C) displacements of organs; (D) transfor- 

 mation of organs or portions of organs; (E) development of new 

 parts in preexisting organs and also of new organs. 



3. When it is a question of new organs, we are always in the 

 presence of more or less advanced dififerentiations of determined 

 somatic regions, which organize into special forms what elsewhere 

 are characteristic of the same regions. 



4. The modifications undergone by a species (or by a higher 

 taxonomic group) are generally numerous and complicated and often 

 functionally coordinated, so that they may involve several organs or 



