DEPARTMENT OF EXPERIMENTAL EVOLUTION. 149 



POULTRY. 



There were maintained 26 breeding pens and 1,624 chicks were 

 hatched. Selection experiments on plumage color were continued. 



SHEEP. 



Nineteen lambs were born, giving additional data on twin inheri- 

 tance, extra nipples, and double horns. 



CONSTRUCTION AND EQUIPMENT. 



Two additional pigeon-houses (making 4 in all) have been completed, 

 and the grading (including concrete walls and steps) has been done. 

 Extensive grading south of the animal house was done and runs put 

 in place for large mammals. Six sets of concrete cold frames were 

 built in the west garden and two concrete service bridges over the 

 ravine. Part of the earth moved in grading was placed on the salt 

 marsh, increasing the garden area, and the sandier part was used for the 

 foundation of a tennis court, near the animal house. A tool-house and 

 shelter, 12 by 18 feet, were finished at the farm. A shelter for summer 

 work with rats was installed on top of the animal house. The fence 

 around the sheep pasture was painted. The south end of the second 

 floor of the Laboratory was remodeled to meet new needs. Metal 

 racks and cages for the rats were made, and numerous small bits of 

 apparatus and cabinet-work made for the various investigators' rooms. 



The largest and most expensive addition to our equipment has been 

 an air-conditioning apparatus to furnish the required temperature and 

 moisture conditions to 4 rooms in the animal house. The general 

 method of refrigeration employed is that of compression of ammonia. 

 The expansion Qf the ammonia in the tubes cools brine. Moisture 

 and dryness in desired amount are seciu-ed and maintained at a con- 

 stant level, as in the warming apparatus. 



