134 CARNEGIE INSTITUTION OF WASHINGTON. 



plants (Amer. Jour. Bot., 7: 62-102, 1921). They find the struc- 

 ture of the trimerous seedhngs fundamentally different from that of the 

 dimerous seedlings, the former being on a plan of 6 instead of 4. But 

 when a large number of seedhngs is examined there is found a wide 

 range of variation in the number and in the combinations of primary 

 double bundles. The plants which are externally dimerous and tri- 

 merous are thus clearly differentiated in internal morphology; but 

 these internal characters are transgressive. It is possible, though rare, 

 to get a trimerous seedling (with 3 cotyledons) that has only 4 vascular 

 bundles in the hypocotyl instead of 6. Papers on the correlation of the 

 number of vascular elements in different regions of the seedling and 

 on the vascular anatomy of hemitrimerous plants are now in press. 



Direction of Whirlinp, in Waltzing Mice. 



Yerkes, in his work with Japanese waltzing mice, has noticed that 

 these animals as a group are divisible into (a) those that made a vast 

 preponderance of their turns in a right-handed or a clockwise direc- 

 tion, (6) those that made a great preponderance of their turns in a left- 

 handed or counter-clockwise direction, and (c) those that were mixed, 

 turning either to the right or to the left with approximately equal 

 frequency. 



In the Lambert strain of Japanese waltzers used by Dr. Little in this 

 Department the same is also true. These mice are directly descended 

 from a single pair of Dr. Yerkes's mice, isolated in 1906. They have 

 been intensively inbred. It is therefore quite striking to note that 

 there exist the three types of waltzers, none having been eliminated 

 by inbreeding. 



A study of the distribution of frequencies of clockwise-turns out of 

 all-turns, based on hundreds of measurements, reveals a trimodal condi- 

 tion, proving that prevailingly clockwise and prevailingly anti-clock- 

 wise individuals are not merely the rare extremes of a variable series, 

 but, on the contrary, constitute types as real as the mixed type. 



It was also found that normal, non-waltzing mice, when recovering 

 from anesthesia with ether, instead of progressing as they normally do 

 in a straight line, ran or turned in circles. Although the proportions of 

 the clockwise, counter-clockwise, and mixed types in this group difTer 

 from those in the Japanese group, there is evidence of the existence 

 of the three types of reaction. In this experiment Dr. Little has had 

 the assistance of Miss D. M. Newman as observer. 



ALTERATION OF THE AVERAGE OF A POPULATION BY SOMATIC 



SELECTION. 



Mechanical Devices for Analyzing Selection. 



The study of mechanical contrivances which possess certain bio- 

 logical analogies was continued by Dr. Laughlin during the year. 

 In the July 1921 number of Genetics there was published an article on 



