82 CARNEGIE INSTITUTION OF AVASHINGTON. 



but not thereto, and also progressively away from the stem form, the 

 two kinds being about equal in frequency. As far as tested, these 

 secondary mutations are stable and homozygous. 



The point of most interest in this series in the year is the increasing 

 evidence that mutability is not a hybrid splitting. Crosses of mutating 

 and non-mutating lines show that in Fi mutation is a recessive, segre- 

 gating in F2 with nonnal non-mutating as the dominant. The results 

 of F2, F3, and F4 in this series will, it is hoped, throw much light upon 

 the mutation phenomena in these cultures. 



ECOLOGICAL ADJUSTMENTS. 



As the result of accompanying changed ecological or environmental 

 conditions in the cultures at Tucson, necessary adjustments of the 

 cultures to the nev/ habitat were made or the culture failed. 

 These reactions are, in our experience, of brief duration, occupying 

 one or two or at most ten generations, and are final; that is, the newly 

 introduced form either can or can not adjust itself to the desert habitat, 

 a decision made in the shortest possible time. Thus far, only savannah 

 and mesophytic habitat species have survived at Tucson, while all 

 rain-forest, monsoon-forest, and moist-habitat types in general have 

 failed. In these the Imiiting factor is water-loss, but the critical stage 

 varies with the species, i. e., L. panamensis egg and first larval stages; 

 L. undecimlineata in hibernation; L. diversa in pupation and in hiberna- 

 tion; L. signalicollis in hibernation. 



In species that do meet the change adjustment has been a graduated, 

 continuous, though often a rapid, reaction, and not a jump to the 

 full accommodation. In the earlier generations only a few pass the 

 critical stage, and these often with difficulty; but the descendants of 

 those that do pass through show increasing adjustment to the new 

 conditions until in some of our older cultures, now in Fic to Fig, the 

 adjustment is complete as far as discoverable. 



Thus far I can discover no evidence that this result is the product of 

 an environmental selection of pure lines, and therefore a selection result; 

 but it is due, as far as I can discover, to accidental positions or circum- 

 stances such that the surviving members, while intensely acted upon, 

 did not receive the action of the environmental force to the extent that 

 would eliminate them. Many accidents of time, of position, and of 

 environmental and ontogenetic progression would give opportunity 

 for exactly this effect. 



The most conclusive and impressive experience which comes from 

 these cultures is that accommodation or adaptation is environmentally 

 directed and limited, and not produced internally in the organism. 

 The "adaptation" is therefore in certain ways molded by and fitted to 

 the environment, and not offered to the environment for selection by 

 internal and orthogenetic forces. 



