DEPARTMENT OF GENETICS. 103 



agreeing with Kiihn's estimate of Daphnia pulex. The material, while diffi- 

 cult of observation, appears capable of count determination in both spermato- 

 cytes and spermatogonia. 



"The dividing cells in embryonic tissue are exceedingly small, and it may 

 be impossible to determine the number in the ordinary cells. The oogonia 

 are readily differentiated in embryos 16 hours after discharge from the brood- 

 pouch, and under favorable conditions their chromosomes should be readily 

 studied. The number of oogonia laid down at the 16-hour stage is about 

 14 to 16. This number more than doubles by the time the embryos are 

 ready to be released. While no counts have been made of the number of 

 oogonia and eggs when the growth stages of the eggs have begun, there seems 

 to be a considerable increase over that of the stage when ready to be released. 



"On account of the inherent difficulties in the material of Daphnia longis- 

 pina, it seemed best to work out the cytology of Moina before continuing 

 the studies of Daphnia longispina. In Moina the sex-ratio is influenced by 

 crowding mothers in bottles, much as in D. longispina. There is much less 

 yolk and practically no coloring matter in the eggs, conditions which favor 

 the study of maturation stages." 



Comparison of Metabolism in the Sexes. 

 In past years this Department has contributed to the knowledge of the 

 relative metabolism in the production of male and female eggs of pigeons. 

 The existence not merely of males and females, but also sex intergrades in 

 Cladocera, added interest to an investigation of the metabolism of the sexes 

 in this group of aquatic organisms. Dr. V. Obreshkove, of Syracuse Uni- 

 versity, spent the summer at Cold Spring Harbor determining the rate of 

 carbon-dioxide production in some of Dr. Banta's stock. The rate of carbon- 

 dioxide production serves as an index of the rate of respiration and metab- 

 olism in general — the life processes of the organism. To measure the amount 

 of carbon dioxide produced in a given time, a modified Osterhout apparatus 

 was used. Dr. Obreshkove reports as follows: 



"The principle involved in the simple apparatus is the colon metric method 

 of hydrogen-ion determination. Carbon dioxide affects hydrogen-ion con- 

 centration. A measure of the time required for the animals to change a 

 constant quantity of indicator solution from one standard hydrogen-ion 

 concentration to a second standard hydrogen-ion concentration is a measure 

 of their rate of carbon-dioxide production. Animals to be tested are placed 

 in a closed tube the color of which accurately matches that of a similar tube 

 which is a standard, containing buffer solution of the same hydrogen-ion 

 concentration, 7.76, and containing the same indicator. The tubes are then 

 gently shaken by tipping them by an apparatus driven by an electric motor. 

 When the color in the tube containing the animals is changed by these 

 animals so that this tube matches in color a third tube containing indicator 

 and buffer solution of a hydrogen-ion concentration of 7.36, the time is recorded 

 (by means of a stop-watch) . Successive readings of different animals (and on 

 different days and by different observers) of the same developmental stage 

 are remarkably consistent. With this apparatus a fine series of determina- 

 tions was obtained for (1) four stages in the developmental cycle of normal 

 Simocephalus exspinosus females, (2) mature males of the same species, and 

 (3) mature females of Moina macrocopa. 



"The very small young just released from their mother's brood-chamber 

 were tested 10 at a time, the time required to produce the standard color 

 averaging 93 minutes and 46 seconds for 10 individuals. Hence for one indi- 

 vidual the mean reaction-time is 937 minutes. For mothers which had just 



