A manual of obstetrics . ow, andthe vital elements, male and female, being brought intoimmediate proximity. The periods of comparative (but notabsolute) immunity are the second week before the expectedappearance of the flow, and the first four months of lacta-tion ; statistics show that insemination occurring duringthese periods is likely to be fruitless. Method of Impregnation.—This question is now posi-tively determined. There is beyond doubt an actual pene-tration by the spermatozoidsof the vitelline membrane ofthe ovum (Fig. 2i), and thispenetration probably takesplace through a minute ope
A manual of obstetrics . ow, andthe vital elements, male and female, being brought intoimmediate proximity. The periods of comparative (but notabsolute) immunity are the second week before the expectedappearance of the flow, and the first four months of lacta-tion ; statistics show that insemination occurring duringthese periods is likely to be fruitless. Method of Impregnation.—This question is now posi-tively determined. There is beyond doubt an actual pene-tration by the spermatozoidsof the vitelline membrane ofthe ovum (Fig. 2i), and thispenetration probably takesplace through a minute open-ing, the micropyle. At leastthis is true of invertebrates,and probably of the rabbit,and, inferentially, the exist-ence of such an entrance inall ova may be assumed. Asto the cause of the mutualattraction of ovum and sper-matozoid little is known. Itis probable that but one spermatozoid finds entrance intothe ovum, and that this accomplishes the work of fertiliza-tion. The ovum, being thus fecundated, proceeds on its. Fig. 21.—Ovum of the Nephelis vulgaris,showing retraction of vitcllus and the pene-tration of the spermatozoa through the vitel-line membrane; X 300. PREGNANCY OR GESTATION. 47 way to the uterus, where it finds permanent lodgement atabout the tenth to the twelfth day after impregnation. Itspoint of attachment is generally high up on the posterioruterine wall near the orifice of one of the Fallopian tubes. ^~,
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectobstetrics, bookyear1
