126 THE EGGS OF MAMMALS 



luteum extracts (Nelson, PMner and Haterius, 1930). Since 

 the pituitary extracts employed by Teel caused marked 

 luteinization of the ovaries of injected animals it is possible 

 that the delay in implantation may be due to excessive 

 corpus luteum secretion. Selye, CoUip and Thomson (1935??) 

 have ingeniously demonstrated that the rat ovary during 

 lactation presumably produces little or no oestrin, so that 

 the hormone-producing tissue of the ovary during lactation 

 is predominantly the luteal tissue. One need not postulate 

 hypersecretion by the corpus luteum during lactation but 

 merely an unbalance in which corpus luteum hormone pre- 

 dominates (thus Selye, Collip and Thomson actually obtain 

 larger corpora lutea in lactating mice when oestrin is 

 injected). 



Wislocki and Goodman (1934) injected a preparation of 

 progestin (after Allen, 1930), for 8 days after mating into 

 two rabbits but no delay of pregnancy ensued. Antuitrin-S 

 and antuitrin-G injected in fairly large amounts during 

 early pregnancy were also ineffective although these prepara- 

 tions induced a fresh ovulation and new corpus luteum 

 formation. The ineffectiveness of progestin in the two experi- 

 ments of Wislocki and Goodman may have been due to an 

 insufficient dosage. On the other hand it is possible that 

 delayed pregnancy is due to an insufficiency of corpus luteum 

 secretion, so that the immediate effect of Teel's extract may 

 be considered the stimulation of oestrin production with 

 inhibition of luteal secretion followed by corpus luteum 

 activity which induced or completed the implantation proc- 

 ess. Hamlett (1935) is in fact of the opinion that delayed 

 implantation is due to hyposecretion of the corpus luteum. 

 He has found (1932) that copulation and cleavage occur 

 in the nine-banded armadillo of Texas during July, and the 

 unimplanted vesicle lies free in the uterine lumen until 

 early November when implantation takes place. Correlated 

 with the quiescent period is a large corpus luteum the cells 

 of which contain few or no secretory droplets or granules. 

 Shortly before implantation vacuolization and lipoidal secre- 



