308 



SCIENCE 



[N. S. Vol. LIII. No. 1370 



cliaracteristic of continental sediments, the 

 local breaks not representing a loss of geologic 

 time of any marked historical value." 



The plants certainly do not uphold this 

 contention, but they do indicate a very con- 

 siderable hiatus between the top of the 

 acknowledged marine Cretaceous section and 

 the inauguration of the Lance. The Laramie 

 is not known within this area, but can it be 

 doubted that it was the interval during which 

 in other areas beds of Laramie age were laid 

 down and subsequently removed in whole or 

 in part? That there was an important inter- 

 val of some kind is also shown by the fact 

 tliat it was sufficiently long for over 60 per 

 cent, of the marine Cannonball fauna to be 

 derived thi-ough modification of the typical 

 Fox Hills fauna. F. H. Knowlton 



PROOF OF NON-DISJUNCTION FOR THE 



FOURTH CHROMOSOME OF DROSO- 



PHILA MELANOGASTER 



During the spring and summer of 1920 I 

 secured genetic evidence that strains of D. 

 melanogaster haploid for the fourth chromo- 

 some had been produced by non-disjunction, 

 and in November cytological verification was 

 obtained. The fact that non-disjunction of 

 the fourth chromosome is known to occur is 

 perhaps the strongest reason for believeing 

 that the aberrations observed by Dr. Little^ 

 may be the consequences of non-disjunction. 

 The direct evidence presented by Dr. Little by 

 no means proves such to be the case, which is 

 unfortunate, considering the ample means in 

 D. melanogaster for checking up this hy- 

 pothesis by means of other fourth-chromo- 

 some mutants (bent, shaven) and especially by 

 direct cytological examination. Probably Dr. 

 Little will include such evidence in his forth- 

 coming detailed report. For the present, his 

 published evidence is in better conformity 

 with the assumption of a less exti'eme eyeless 

 allelomorph, or of a dominant fourth-chromo- 

 some " minus " modifier. On the non-dis- 

 junctional view selective reduction of the 

 three fourth chromosomes present is required, 

 but there is no obvious reason why E and e 



1 Science, 53 : 167. 



should always go together in the manner 

 assumed. A simple explanation is supplied 

 on the weak-allelomorph view, for Ee is the 

 weak allelomorph and the selective reduction 

 Ee — e is simply segregation in the e^ — e 

 compound. Lhikage supplies the explanation 

 on the modifier view, for the E is then a domi- 

 nant minus modifier in the fourth chromo- 

 some, and Ee — e is simply M°e — e. As far 

 as can be judged from the short account given, 

 all the observed ratios are in conformity with 

 either of these views. Thus, Dr. Little has not 

 proved by direct and available means that the 

 case is actually one of non-disjunction, nor 

 has he proved it negatively by excluding well- 

 recognized alternative hypotheses which are 

 equally valid and even more in harmony with 

 the facts of the case as stated. 



C. B. Bridges 



SURVEYING FROM THE AIR 



The article on " Surveying from the Air," 

 December 17, 1920, is a summary of the work 

 of the Coast and Geodetic Survey along the 

 lines of aerial photography, and of necessity 

 does not go into the requisite detail regarding 

 the reasons for making tlie following state- 

 ment: 



These experiments proved very conclusively that 

 photographs from the air, using present-day equip- 

 ment, are of little practical value to the hydro- 

 grapher. 



This statement has been nojed by Mr. Willis 

 T. Lee, of the U. S. Geological Survey in 

 Science, February 18, 1921, who cites Comptes 

 Eendus Tome 169, October 27, 1919, in which 

 mention is made of experiments near Brest 

 where successful photogi-aphs were obtained 

 of the bottom at a maximum depth of 17 

 meters. 



During the experiments at Key West, the 

 results of which were the only ones then 

 known to me, occasional successful photo- 

 graphs of the bottom were obtained in depths 

 of 35 feet and less. No attempt was made to 

 photograph at greater depths. When the con- 

 clusion regarding the " practical value " of the 

 photographs was arrived at, all factors re- 



