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SUMMARY OF CURRENT RESEARCHES RELATING TO 
death of the embryo are thus causally associated, although the relative 
inadequacy of a particular shell is but loosely correlated with the death 
of the particular embryo contained within it. An unknown and more 
deeply seated cause is responsible for both the occasional inadequate or 
irregular shells and the numerous early deaths of embryos. Experience 
indicates that among pigeons the thin shells and associated early-dying 
embryos often occur after a long series of normal shells and viable 
young. After abnormally rapid reproduction there may be many such 
cases. The second egg of a clutch may be worse than the first, measured 
by the relative rate of the loss of water vapour through the shell. The 
second eggs are more likely to receive a slightly reduced relative amount 
of shell material. There may be some depletion in the mother’s calcium 
supply ; but there is some disorder in both ovum and oviduct. Several 
possible nutritional deficiencies have been investigated, but the real 
cause of the perturbation remains unknown. J. A. T. 
Differential Survival of Male and Female Dove Embryos in 
Increased and Decreased Pressures of Oxygen. — Oscar Riddle 
( Proc . Soc. Exper. Biol, and Medicine, 1920, 17, 88-91). If female 
embryos have a lower metabolism — i.e. lower minimum oxygen require- 
ment — than males, the female embryos should withstand diminished 
pressures of oxygen somewhat better than male embryos. And male 
embryos should be better able to withstand an increased concentration 
of oxygen. Reduced metabolism induced by cooling should perhaps 
prove more harmful to the male embryos. The results of the experi- 
ments are not wholly decisive, but they give some evidence that sex is a 
factor in survival. The males best survive increased pressures of oxygen, 
and the females best survive decreased pressures and cooling. J. A. T. 
Hermaphroditism of a Croaker. — C. M. Breder, Jun. ( Zoologica , 
1922, 2, 281-4, 1 fig.). In a specimen of Micropogon undulatus two 
perfect ovaries and two perfect testes were found. The fish seemed to 
be about five years old, and had therefore passed through at least one 
spawning season. The case suggests functional hermaphroditism. It 
is possible that self-fertilization occurred, or double mating. Most 
previous records of hermaphroditism in fishes tell of one set of gonads 
being much in advance of the other, but the ovaries and testes were 
practically equal in development in this case, J. A. T. 
