BIOLOGY. 323 



parents (spermatogenesis), an estimate based on 400 young. Female parents 

 in 115 young have given 9 cross-overs, which is 7.8 ±3.1 per cent. The 

 numbers are as yet insufficient to show conclusively whether females produce 

 more or fewer cross-overs than males. Certain it is, however, that both 

 sexes produce cross-overs in all cases of linkage thus far demonstrated in mam- 

 mals. Since the same is true in plants, it seems to be an exception rather than 

 a rule that has been encountered in Drosophila, where crossing-over occurs 

 only in females. 



Dr. W. L. Wachter has assisted in the linkage investigations with mice and 

 rats. 



Kofoid, Charles A., University of California, Berkeley, California. Investi- 

 gation on intestinal protozoa. 



The scientific results attained have been : 



1. The discovery of amebse in bone marrow in arthritis deformans. 



2. The discovery of amebse in lymph glands in Hodgkin's disease. 



3. The finding of amebae in abundance in the capillaries in the margins of 

 intestinal amebic ulcers. 



4. Analysis of the process of mitosis and determination of chromosome 

 number in two human intestinal amebse. This affords a critical morphological 

 basis for the accurate identification of amebse in human tissues. 



5. The morphological analysis of the process of mitosis in giardia enterica 

 from man. 



6. A considerable amount of detailed information on a number of human 

 intestinal amebse and flagellates and amebse which awaits supplemental 

 material and analysis before publication. 



7. The establishment of craigiasis as a human disease with an etiological 

 factor, craigia hominis. This has been denied by English investigators 

 without adequate data. 



8. The finding of amebse in non-healing ulcers of the skin. 



9. Critical evidence as to the necessity of repeated examinations for detec- 

 tion of intestinal infections. It has been and is in some quarters the custom 

 to rely upon one examination. 



10. The discovery of the prevalence of family infections. 



11. The statistical analysis of about 20,000 examinations of over 5,000 

 persons for intestinal parasites. 



For papers published during the past year, see page 25 of the Year Book. 



Mann, Albert, Washington, District of Columbia. Continuation of investiga- 

 tions and preparations for publication of results of work on Diatomacece. 

 (For previous report see Year Books Nos. 18-20.) 



To keep this report within its proper limits it will be necessary to give almost 

 exclusive attention to the important trip along the Pacific Coast, made in 

 June to September 1921, a forecast of which was included in my last report. 

 The purposes of this trip appear to have been accomplished, namely, a visit 

 to all the biological stations along the coast and to the principal fossil diatom 

 deposits of California, not so much to carry on research as to consult with the 

 scientists at these places, to awaken more interest in thorough diatom study, 



