THE GROWTH OF THE OVUM 33 



fully grown is 125 microns and in the rat (Parkes, 1931) 

 the maximum diameter of the ovum is attained when the 

 folhcle is 160 microns in diameter. Full growth of the 

 ovum, then, is attained just before the time of antrum 

 formation which begins in rats and mice in follicles having 

 diameters of about 200 microns. We may therefore deduce 

 that the ova of hypophysectomized animals attain the di- 

 mensions of the mature ova in o\ailating animals, and that 

 the growth of the ova (and early follicular growth) is inde- 

 pendent of the hypophysis. 



This conclusion is supported by various independent lines 

 of evidence. Aral (1920a) found that ova over 60 ijl in diameter 

 appear in the ovaries of rats between the 15th and 20th days 

 of age. Engle (1931a) found pseudomaturation spindles, 

 which appear only in ova of full size, first evident in 16 day 

 old mice and no follicles more than 180 /z in diameter in 

 14 day old mice. Smith and Engle (1927) found that 10 day 

 old mice treated with gonad-stimulating pituitary implants 

 had to have daily implants for 5 days in order that full 

 ovarian response should be attained, whereas 17 day old 

 mice showed full response in 36 hours to 3 days. Corey 

 (1928) found practically no ovarian response to pituitary 

 extracts in rats until after the 15th day, and Selye and 

 Collip (1933) found no follicular maturation in 6 to 12 day 

 old rats treated with anterior pituitary-like hormone (see 

 also Zondek, 1931). In rabbits (Hammond and Marshall, 

 1925) the antrum develops later than the 10-1 1th week of 

 life. Hertz and Hisaw (1934) were able to obtain definite 

 follicular response to follicle-stimulating and luteinizing hor- 

 mones only in juvenile rabbits (12 to 13 weeks old), not in 

 infantile rabbits. Casida (1935) reports that pig ovaries show 

 definite response to pituitary hormones only when antrum- 

 containing follicles are present. 



Nonetheless, fully potent pituitaries are present in 5 to 

 8 day old rats (Smith and Engle, 1927; Lipschutz, Kallas 

 and Paez, 1929) as judged by their effects in transplantation 

 to immature recipients. It would seem, then, that the at- 



