ZOOLOGY — PEARL, TOWER. 249 



Paramecium, yet by proper environmental conditions it is possible to obtain 

 a population which, in spite of its selected ancestry, shows just as great varia- 

 bility as does a " wild" population of unselected ancestry. A paper dealing 

 with variation and correlation in Chilomonas has been completed and is now 

 in press. 



(5) The material on variation in the whitefish (Coregonus), to which 

 reference has been made in previous reports, has been reduced, and a paper 

 giving an account of the results will be ready for the press soon, 



(6) Several minor papers dealing with specific problems of variation and 

 correlation have been completed during the year, and have either appeared or 

 are now in the press. 



In continuation of the investigation of the problems of variation and 

 correlation, it is proposed to carry forward the work along two principal 

 lines, viz, (a) Vv'ork on Protozoa, and (d) analysis of the laws of growth. 



Tower, "William L«, University of Chicago, Chicago, Illinois. Grants Nos. 

 181 and 251. Experimental investigations of the production ayid preserva- 

 tion of new character races and species hi insects, (For previous reports 

 see Year Book No. 3, p. 141, and Year Book No. 4, pp. 286-2S8.) $1,945. 

 Abstract of Report. — The studies with Leptinotarsa since 1904 have been 



along four chief lines : 



1. Pedigree breeding and the experimental production of new races. 



2. Transplantation experiments in nature in southern Mexico. 



3. An experimental statistical investigation of natural selection. 



4. The ecology of the material under investigation. 



While investigations under these grants have been largely concerned with 

 the genus Leptinotarsa, it seemed desirable to extend them to the related 

 genera of the essentially American group. This was begun in the year 1905 

 and has been continued during the past year. The work upon these other 

 forms has been largely preparatorj^ consisting in a compilation of all known 

 data concerning their distribution, variation, habits, etc. Preliminary pedi- 

 gree cultures of different species of Calligrapha, Zygogramma, Stilodes, 

 Labidomera, Dorj^phora, and Melasoma are being made, and this material 

 will later form the source of supply for experimental studies. 



General results derived fro7n these investigations. — In these investigations, 

 which have now been in progress for more than twelve years, an attempt has 

 been made to view animal evolution in a restricted group from as many 

 viewpoints as possible and thus to be able to correlate and check the results 

 obtained from different minor parts of the main problem. 



The investigation of the phenomena of variation in its diverse aspects has 

 given the general result that, as far as this material is concerned, there is 

 no indication of indeterminate variability — that is, all variations thus far 

 studied are in few directions, and in the case of any particular species are 

 determinate irrespective of their size or behavior in inheritance. Variations, 



