68 CARNEGIE INSTITUTION OF WASHINGTON. 



Evolution of the Chrysomelid Beetles, by W. L. Tower. 



A series of experiments has been under way at Tucson, almost 

 from the beginning of the work, consisting of the intercrossings of 

 two or more species without the removal of any of the progeny from 

 the population, with the result that there were produced in a few 

 generations, as previously reported, stable stem-stocks which were 

 the product of the synthesis of all of the characteristics derived from 

 the different parents. Several such stocks are now at Tucson, 

 some of which, under the conditions under which they arose, have 

 remained absolutely constant, and, moreover, on being removed to 

 Chicago and tested under different conditions, they have thus far 

 shown no tendency to break up or to give as extracted forms any of 

 the original parental types or characteristics. 



In plate 3, figures 4, 5, and 6, are shown stable stem-forms that 

 have been thus created. That shown in figure 4 is the product of 

 a synthetic union of L. decemlineata Say, L. multitceniata Stal, and 

 L. oblongata n. sp. Some of the stocks, when given proper treatment, 

 especially by changed environic factors, so that the conditions of 

 existence are optimum, can be made to break up, and those which 

 are thus made to break up do so in a manner that is precisely like 

 that which de Vries found in Oenothera lamarckiana. 



One of our most interesting series is that represented in figure 4, 

 produced by the union of L. decemlineata Say and L. oblongata n. sp., 

 in which there have appeared thus far about 15 distinct types, some 



Description of Plate 3. 



1. L. multitceniata Stal. A normal average form. 



2. L. decemlineata Say. Normal stock from Chicago. 



3. L. oblongata n. sp. 



4. A mutating stem stock C. H. 15.7, made up of the synthesis of the first two parent 



species L. multitceniata and L. decemlineata. 

 .5. Another stable stem stock which arose as the product of the synthesis of all three 

 types. 



6. A mutating stem stock of a different origin, composed of L. decemlineata and L. 



multitceniata. 



7. An elongate mutant that appears in the line A, that breeds true on first appearance. 



It resembles L. oblongata in shape, but in no other respect, and the form exhibited 

 is apparently a new character that arose as the result of this operation. 



8. Another mutant that arose from the same series of experiments, showing in pronotal 



color conditions that come in with the L. multitceniata stock, but which have not 

 been present in that stock for many generations. 



9. Another mutant from the same stock, also breeding true, showing new combinations 



from both stocks and the loss of color on the elytron, giving the appearance of a 

 semi-albinic type. 



10. Another type of mutant appearing from the same series of experiments, also breeding 



true. 



11. A mutant exhibiting the characters of L. melanothorax on the head and pronotum, 



which could only have come in the line through the L. multitceniata parents. 

 The L. multitceniata used in this experiment, however, was a pure strain in which 

 L. melanothorax was not known to exist. The reappearance of the L. melano- 

 thorax character, however, in this mutating strain shows either that the L. 

 melanothorax character is carried in some condition for a long period of time, or 

 else that there has been produced in this mutation a resynthesis of the character 

 which is L. melanothorax in all respects. 



