122 CARNEGIE INSTITUTION OF WASHINGTON. 



the numbers of doors of different kinds that they entered. The data, as 

 tabulated, entirely obscure these reaction tendencies, yet these would give a 

 different and possibly fairer test of the rats than is afforded by their relation 

 to an arbitrarily estabhshed standard. The graphic records of each individual 

 trial provide this information; from the record sheets it will be possible to 

 classify the successful types of reactions on an absolute basis; how consistently 

 the different types of reaction were shown; how sensitive the animal to 

 extraneous circumstances, to the operation of the apparatus; thus, a study of 

 the general motor tendencies and many other exceedingly interesting and 

 important side-hghts will be afforded. 



"That the maze and the multiple-choice apparatus do not give the same 

 results when the tests and controls are compared does not weaken the sig- 

 nificance of the conclusions in either case. The problems are of a different 

 nature and require different mental processes for their solution; the rats solved 

 the one v/ith ease, the other was not solved in the number of trials allowed. 

 Longer training would have given greater success and probably mastery of at 

 least one of the multiple-choice problems. It is entirely possible that the final 

 perfecting of the solution would bring out differences between the tests and 

 controls, however much alike their rate of learning in the beginning. On the 

 other hand, if the perfoimance in the early part of the learning process should 

 be a true sample of the whole process, it is equally simple to suppose that the 

 alcohol may have modified the nervous mechanism involved in learning the 

 maze and have had no influence at all upon the processes that are involved in the 

 solution of the multiple-choice problem. So the conclusion stands that the 

 maze brings out differences between the tests and controls, and the multiple- 

 choice apparatus, as far as the training went, did not bring out these or other 

 differences." 



SIGNIFICANCE AND CONTROL OF SEX. 



COMPARATIVE METABOLISM OF SEXES IN PIGEONS. 



Dr. Riddle has extended his studies on the metabolic differences 

 between the eggs that give rise to the two sexes to a study of the dif- 

 ferences in the metabolism of male and female embiyos. He found it 

 difficult to devise a satisfactory method of measuring these differences 

 but finally adopted the following: He undertook to subject, during an 

 entn-e year, all, or practically all, of the embryos produced by the ring- 

 doves and common pigeons of our collection to reduced and to increased 

 concentrations of oxygen, or to expose them to protracted periods of 

 cold, and to observe the relation of sex to survival under these con- 

 ditions. 



Theoretically, if female embryos have a lower metabolism than male, 

 the female embryos should withstand diminished pressures of oxygen 

 better than male embryos. Similarly, since it liad been earlier learned 

 that high pressures of oxygen result in the death of some embryos, the 

 male embryos should be somewhat better able than female embryos 

 to withstand an increased concentration of oxj^gen. Again, if males 

 have a higher metabolism than females, the reduced metabolism in- 

 duced by cooling should prove more harmful to the male embryos. 



Embryos aged 3 minutes (after laying) to 12 days were used; and 

 most frequently the age was between 1 hour and 4 days. Increased 



