PARIERACEYY step syetetse sxe cheter sete Siessioie ie ctstels'iaiata avs' a/efea suave, ehasojereyato Mal terete ee enctele tei oteeranete Vii CHAPTER I MEER GROUPSPANDENAMESTORNIVIACAOUMESH: sae ceeieiei eile ae eee nie ean ie

No abstract

The yolk-free peripheral aiid cwit,rnl zones and t,hc yolk-laden submarginal zone are well shown ( X 607).4 IJterinc ovum, with pronuclei, No. 54 (2). Thc specimen is sorricwhat :kbnormiil i n the possession of t h n thirrl t>od?. i.1) xdjncrnt t o on(: of the pronuclci ( X 790).Tuba1 ovum, No. 56 (10).

AUTHOR'S ABSTRACTThe breeding season of the opossum a t Austin. Texas. begins in J a n u a r y , following a three months' anoestroun period. The modal point for ovulation days is reached in the third week.The rate of intra-uterine development was investigated chiefly by surgical removal of one uterus, noting the stage attained hy the ova therein and allowing the surviving uterus to incubate its ova a precalculated period of time. Unique charts epitomize the results. The primitive-streak stage is completed, the medullary groovc a n d chorda hegin a t seven a n d one-half days post coitum, seven days post ovulationem, leaving only five a n d one-half days' actual development of the emhryc to birth. The rate of development is compared with Entherian mammals.The curve of postnatal Srowth hns the shape of embryonic growth curve of higher mammals. The ryes a n d lips open, a t ahout fifty days (young the size of mice). At this time the young leave the teat for the first time, h u t are not weaned for ahout thirty days more. Soon a f t e r weaning, t,he mother may become pregnant again. At ninety to one hundred days (young size of large r a t s ) , the young may begin to shift for themselves. P 148 P P W Text fig. C Chart 1, to show rate of development from one stage t o another, both stagrs taken from the same female, The numbers are the protocol c2 the intervening intervals of time controlled t o the minute. (For details see text, p a r t 11.) numbers of the animals furnishing the eggs and embryos.