BIOLOGY — CHEMISTRY. 331 



shows that the sequence is the same in both, but that the amounts of 

 crossing-over are somewhat different. 



Among the mutants found in D. simulans is one, located in an auto- 

 some, that causes characteristic male parts to appear in the genitalia 

 of the female. Such individuals fall under the general category of 

 intersexes — the occurrence of which, in other forms, has attracted much 

 attention in recent years ; in the present instance it has been shown that 

 the intersex is due not to disturbances in the ordinary sex-determining 

 mechanism, but to a mutation that took place in an autosome, i. e., 

 not even in a sex-chromosome. 



The stocks of Drosophila that are kept on hand and serve as our 

 working material number nearly 200. The stocks represent only those 

 types and combinations that have been found valuable for our work, 

 and do not include all the mutant types that have appeared during 

 the past few years. Mutants whose viability is poor are not kept 

 longer than is necessary to place them on record. Those whose 

 separation from other stocks or from the wild-type is uncertain or 

 laborious are also allowed to go. To avoid the necessity of selection 

 in every generation, in cases in which one or the other sex is sterile or 

 dies, we have made use of the principle of balanced lethals. As a 

 result of the balancing, such stocks appear to breed true, although they 

 are in reality permanent hybrids. 



In connection with the work of the year, it may be noted that : Dr. 

 J. F. Nonidez has completed a careful study of the physiology and 

 structure of the reproductive organs of D. melanog aster; Dr. Shelley 

 R. Safir has completed his work on primary non-disjunction ; Mr. L. C. 

 Strong has worked out the location of the mutant roughoid; Mr. H. H. 

 Johnson has discovered and worked out a mimic of vermilion and 

 scarlet, called cardinal; Dr. Mary B. Stark has continued her work, 

 though not in our laboratory, on the lethal tumor, and has discovered 

 also a benign tumor that behaves as a Mendelian character; Mr. D. E. 

 Lancefield has carried out work on the genetics of D. ohscura, which 

 has a different chromosome group from that of D. melanog aster, and 

 which promises results of great importance. 



CHEMISTRY. 



Morse, H. N., Johns Hopkins University, Baltimore, Maryland. Measure- 

 ment of the osmotic pressure of solutions. (For previous reports see Year 

 Books Nos. 2-16.) 



During the past year the work on osmotic pressure has been along 

 two lines: first, the perfection of a suitable method for the measure- 

 ment of osmotic pressure which would permit accurate measurements 

 of high pressures and at the same time the rapid attainment of equi- 

 librium pressure; secondly, the perfection of the osmotic membrane 



