286 REPORTS ON INVESTIGATIONS AND PROJECTS. 



It is expected that a paper giving the detailed results of all the 

 studies on variation and correlation mentioned above (as well as others 

 mentioned in the report of last year) will be submitted for publication 

 during the coming year. 



Stevens, Nettie M., Bryn Mawr College, Bryn Mawr, Pennsylvania. 

 Grant No. 177. hivestigation of problems relating to sex detcr- 

 minatio7i. $1,000. 



Abstract of Report. — The experimental work on Aphids has not 

 as yet given positive results. Histological investigation of the 

 germ cells of Aphis roscB and Aphis cenotherce was completed in De- 

 cember, 1904, and the results published in the Journal of Experi- 

 mental Zoology, vol. II, No. 3, August, 1905. The results of a 

 comparative study of the spermatogenesis of several species of in- 

 sects, with especial reference to the " accessory chromosome," are 

 being published by the Carnegie Institution of Washington as Pub- 

 lication No. 26. The most important point in the latter paper is 

 the discovery in Tenebrio molitor of a form in which sex determina- 

 tion by a dimorphism of the spermatozoa, not due to the presence 

 of an " accessory chromosome," seems probable. 



Tower, "William L., University of Chicago, Chicago, Illinois. Grant 

 No, 251. Experiynental investigations of the production and pres- 

 ervation of new character races and species in insects. (For first 

 report see Year Book No. 3, p; 141.) $1,500. 



Abstract of Report. — In the work Mr. Tower has employed Lepti- 

 notarsa undecimlineata, signaticollis, miiltitcBniata, oblongata^ dilecta, 

 and violescens and Epilachnia in Mexico, and at Chicago L. signa- 

 ticollis, decemlineata, and undeciinlineata. The experiments on Lepti- 

 notarsa have reached conclusive results. Four clearly distinguished 

 classes of variations have been found — gonogenic, gamogenic, em- 

 bryogenic, and somatogenic. 



In Leptinotarsa, as far as evidence is in hand, it appears certain 

 that new and permanent characters do not arise at any other period 

 of life than in the germ cell or gonogenic stage. In four species of 

 Leptinotarsa the important fact has been demonstrated repeatedly 

 that it is in the growth period of the germ cells in both ova and 

 spermatozoa that permanent modifications are produced. 



Permanent modifications of several species of Leptinotarsa have 

 been produced in two ways : {a) By sudden large variations, and {b) 

 by slow accumulations of small variations, the variations in both 

 cases being gonogenic. From experiment and also from observa- 

 tion in nature, the evidence is that in Leptinotarsa the origin of 



