tract. The controlled temperature group showed no drop in sperm 
concentration during the first fall as was found in the males 
housed outdoors. During the second winter, the outdoor group 
produced no semen but by the following spring, they exceeded the 
controlled temperature group in sperm concentration. This in- 
dicated to the authors that a "rest period" was essential for 
normal sperm production in the turkey male. There was less fluce 
tuation in size of the seminiferous tubules in males housed at 
a constant temperature. 
ad) Effect of the "scrotum", 
The thermo-regulatory function of the scrotum in mane 
mals is well known. Sterility usually results when the testes 
are retained in the body cavity. Birds do not have a structure 
homologous to the mammalian scrotum and it has remained some- 
what of a mystery why fertility of birds should be high when the 
testes are held within the body cavity. 
It has been postulated that the posterior abdominal air 
sacs may exert a colling effect on the testes and,in effect, 
assume the function of a scrotum. This was tested experimentally 
by Herin, Booth and Johnson (1960) by surgically removing the air 
sacs, and by removing air sacs and insulating the testes with 
surgical cotton. They found no differences in semen quality be- 
tween treated birds and controls. Semen quality was measured on 
the basis of motility, concentration, morphology and per cent 
of dead sperm cells. They further found no differences between 
testicular, air sac and rectal temperatures. They concluded that 
the air sacs do not c6ol the testes of the rooster. 
In passerine birds, there is another structure which 
may have a thermo-regulatory function. In these birds, during 
the breeding season, there is an extensive development of the 
cloacal region produced largely by growth and coiling of the 
lower end of the vasa deferentia. The structure closely re- 
sembles a scrotum and testes from external appearance. Wolfson 
(1954 and 1960) has obtained temperature measurements of the 
body cavity (taken in the large intestine) and of the cloaca in 
four passerine species, In each species studied, cloacal temper- 
ature, in the immediate vicinity of the “scrotum” was seven de~ 
grees Fahrenheit cooler than the temperature of the body cavity. 
Wolfson postulated that in passerines this structure serves as a 
thermo-regulator for maintenance and maturation of sperm. This 
hypothesis has not been tested experimentally, but such testing 
would no doubt be of considerable interest and might throw 
additional light on this perplexing problem. 
e) Effect of chemicals. 
Few recent reports have been located in which a drug 
or chemical was found to affect the sustentation of sperm adverse- 
7 
