ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 453 



There is no tendency for the first eggs to produce exclusively males, and 

 the second eggs females. As regards determination of sex, the facts 

 seem to indicate that sex in pigeons is determined according to the laws 

 of chance. 



The mean time of laying of the first egg is about 5 p.m., and of the 

 second egg about 1 p.m. of the second day following. The mean 

 interval is practically forty-four hours, but it decreases progressively in 

 the months from February to July inclusive. The mean time of hatch- 

 ing of the first egg is 16*5 days after the laying of the second. The 

 mean time of hatching of the second egg is seventeen days after it is 

 laid. The time from laying to hatching of the first egg is nearly a day 

 and a half longer than for the second egg. This is probably because 

 the first egg receives very little incubation until the second is laid. 



When the eggs do not hatch they are seldom abandoned at the end 

 of the normal period of incubation, but the birds sit on for an average 

 of six days after the normal period, making the mean total time of 

 incubation (when the eggs do not hatch) twenty-three days after the 

 laying of the second egg. This continuance of incubation beyond the 

 normal time under such circumstances constitutes " a factor of safety " 

 in the incubating instinct. The number of days required for the young 

 to hatch being variable, "nature, rather than drawing the line too 

 closely, makes allowance for the extremes." A pair of Mourning Doves 

 (Zenaidura macroura carolinensis) continued to sit on substituted eggs 

 for four days after their own had hatched in an incubator. 



Growth of Body and Organs of Albino Rats fed with Lipoid- 

 free Ration.* — Shinkishi Hatai finds that lipoid-free ration diminishes 

 the normal rate of growth. The weight of the central nervous system 

 is reduced by about 2 p.c. The percentage of water in the longer bones 

 is increased by 5 p.c. The testes showed not only a deficiency of 44 p.c. 

 as a result of six months of the lipoid-free diet, but there is also a clear 

 indication of actual loss of weight (23 p.c), i.e. there is marked atrophy. 

 The ovaries were reduced in weight by 17 '4 p.c, but growth was con- 

 tinuous and there was no loss of gland. A curious result is noted, 

 among many others, that on the lipoid-free diet, as well as in various 

 forms of underfeeding, and after long-continued exercise, the rats 

 become remarkably resistant to the lung infection which appears in the 

 controls. 



Weight of Rats at Birth. t — Helen Dean King finds that the body 

 weight of albino rats at birth differs considerably in different strains. 

 The weights for the males range from 2' 6-7* 5 grm. ; those for the 

 females vary between 2*7 grm. and 5*9 grm. As a rule, in any litter 

 individuals of the same sex are practically of the same size and body 

 weight. 



The body weight depends upon a number of factors that are more 

 or less closely related. 1. The offspring of older females tend to be 



* Anat. Record, ix. (1915) pp. 1-20. 

 t Anat. Record, ix. (1915) pp. 213-31. 



