DEPARTMENT OF GENETICS. 123 



own genetic material, but because it strongly supports Lecaillon's report of 

 parthenogenesis in the fowl. The mode of origin of the subgerminal cavity 

 as this could be learned from pigeon eggs is of real interest to developmental 

 physiology. The results which have been written and sent to press were 

 abstracted as follows: 



"Incubated unfertilized pigeons' eggs acquire a fluid-filled space in the 

 region normally occupied by the subgerminal cavity, and another — peripheral 

 to the germ disk — beneath the vitelline membrane. This increase by osmosis 

 of its water-content at the expense of the surrounding albumen begins in 

 fertihzed and unfertilized ova alike as soon as the ovum is hberated from the 

 ovary. This increased fluidity is observable at all points immediately within 

 the vitelline membrane and in the space normal to the subgerminal cavity. 



"Early cleavage stages occur parthenogenetically in the pigeon's egg. 

 Cleavage proceeds only to a stage approximately equal to that attained 

 10 hours after fertilization in normal development. The degenerative 

 changes which follow are closely confined to the segmented region, and these 

 are accompanied by a pronounced increase of fluid beneath the segmented 

 area. The development, therefore, stops at a stage preceding that at which 

 the subgerminal cavity normally arises, but the cavity forms nevertheless. 

 This cavity in such eggs, therefore, arises not as a result of 'development' but 

 as a result of a progressive increase of water within the ovum. The origin 

 of the subgerminal cavity is thus given a purely mechanical explanation." 



Relation of Age, Sex, Species, and Certain Diseases to the Blood Sugar 



OF Pigeons. 



After Dr. Riddle found the measurement of the sugar of the blood a most 

 convenient method of studying certain metabolic aspects of sex and of 

 reproduction in pigeons, it became necessary to learn the sources of error 

 and variability in this material. In collaboration with Dr. Honeywell he 

 has made about 1,400 sugar determinations. As a result of this study it has 

 been possible to eliminate several sources of error from their own published 

 data; to demonstrate some hitherto unrecognized sources of error in blood- 

 sugar determinations; to evaluate the relation of age and sex to the normal 

 blood sugar in the pigeon better than it has been done in any other species, 

 with the possible exception of man; and to supply, for this aspect of the carbo- 

 hydrate metabolism, the fullest data now available for any order of animals. 



OTHER INVESTIGATIONS. 

 Physico-chemical Properties of Plant-Tissue Fluids. 



As has been emphasized in preceding reports, the cellular fluids represent at 

 the same time the product and the environment of the protoplasm. It is 

 under the influence of these fluids that all the vital processes, cytoplasmic 

 and nuclear, must take place. 



A series of investigations by Dr. Harris and a number of collaborators 

 during the past several years has shown wide variations in the physical and 

 chemical properties of plant-tissue fluids. Such properties as osmotic con- 

 centration, specific electrical conductivity, hydrogen-ion concentration, 

 and the concentration of other ions have been shown to differ not merely from 

 flora to flora, when these are growing under different environmental condi- 

 tions, but to be characteristic of species so closely related that genetic studies 

 may be made upon them when growing under the same conditions. 



