A greater pituitary activity in general was indicated 
in this study since there was also an increase in thyroid and 
adrenal weight in birds grown in the dark environment. fThere ig 
considerable evidence that birds become refractory to light by 
an over-stimulation of the pituitary which becomes exhausted of 
gonadotropic hormones (Miller, 1948, 1949). 
53e Nutrition 
Another factor which may be considered as part of the 
bird's environment is nutrition. Parker and McSpadden (1943) 
found that a reduction in food consumption curtails the pro- 
duction of spermatozoa by Rhode Island Red chickens. A de- 
ficiency in essential feed components may lead to low fertility 
or sterility. A deficiency of Becomplex vitamins leads to teste 
icular degeneration in pigeons. Thiamine appears to be more 
important for testis maturation than riboflavin. When chickens 
are fed for a prolonged period on a diet deficient in vitamin E, 
involutionary changes may occur in the testes, with degeneration 
of cellular elements in the reverse order from which they are 
formed (Harris et al., 1954). Birds as compared to mammals are 
very resistant to vitamin E deficiency. The part of the germinal 
cellaffectedby vitamin E deficiency appears to be the fat or 
fatty acid bodies within the germ cells (Adamstone and Card, 
1934). Vitamin EB appears to have direct effect on the pituite 
ary, since Herrick et al. (1952) found considerable evidence of 
less gonadotropin and fewer basophilic cells. 
4. Genetics 
Since the spermatozoan itself is the means whereby 
the traits of the sire are conferred upon the sons and daughters, 
it is not surprising that genetic factors may alter the normal 
spermatogenesis. Jones and Lamoreux (1942) studying high and 
low fecundity strains of White Leghorn males by histological 
examination of the testes, found that there were more metaphase 
plates and spermatozoa present in the seminiferous tubules of 
the testes in males of the high fecundity strain. It appears 
from this investigation that the rate of sperm cell formation is 
as much under the influence of heredity as is the rate of egg 
formation. Goodwin et al. (1955) suggested that individual 
differences in pituitary output of gonadotropin is under the 
control of genes. 
The phenomenon of parthenogenesis has been extensively 
studied by Olsen (1960a, 1960b) in turkeys. He found that all 
parthenogenetic embryos were males and of the few that hatched 
and reached maturity, three produced spermatozoa and one sired 
offspring. This one male was used to inseminate 7 virgin:hens 
which produced 189 eggs of which 49.7 per cent were fertile and 
85.1 per cent of the fertile eggs hatched. The poults were 
76 
