BIOLOGY OF EGGS AND IMPLANTATION 



827 



observed after ovariectomy. Injections of 

 corjius luteum extract into the operated ani- 

 mals prevented degeneration of the ova. 



Current investigations on fluids of the 

 rabbit oviduct have shown that the secre- 

 tions of the upper, fimbriated third are nec- 

 essary for normal enlargement of the blasto- 

 cyst (Bishop, unpublished data). The 

 oviducts of pregnant females and castrates 

 who have received progesterone secrete co- 

 pious quantities of fluids. If these fluids are 

 prevented from entering the uterus about 

 the 5th day, by double ligation, the blasto- 

 cysts remain small and do not reach their 

 normal size by the 8th day or the time of 

 implantation. 



If fertilized ova of the Muridae are pre- 

 A-ented from entering the uterus, either by 

 ligation of the oviduct or by the administra- 

 tion of hormones which inhibit the normal 

 jiropulsive mechanism of the tube, the eggs 

 develop to the blastocyst stage before de- 

 generation begins (Burdick, Whitney and 

 Pincus, 1937; Burdick, Emerson and Whit- 

 ney, 1940; Alden, 1942d). The occurrence 

 of tubal pregnancies, especially in the hu- 

 man female, indicates that under some cir- 

 cumstances development may continue 

 within the oviduct beyond the stage of nor- 

 mal implantation. 



IV. Fertilization and Implantation 



Fertilization involves the penetration of 

 a fully developed egg by a motile, mature 

 spermatozoon, and the subsequent forma- 

 tion, growth, and karyogamy of the sperm 

 and egg nuclei. An integral part of this 

 process is the physical act of penetration of 

 the spermatozoon into the "karyocyto- 

 plasm" which results in the "activation" of 

 the egg. The classical experiments of Loeb 

 (1913) in the invertebrates and Rugh 

 (1939) in amphibia have shown that "ac- 

 tivation" does not depend on a specific prop- 

 erty of the spermatozoon, but may be ef- 

 fected by chemical, mechanical, or physical 

 stimuli (see also Wilson, 1925). Unfertilized 

 mammalian eggs may likewise be activated 

 by a variety of stimuli, but ordinarily do 

 not proceed far in embryonic development 

 (Pincus and Enzmann, 1936, Chang, 1954, 

 1957. in the rabbit; Thibault, 1949, Austin, 

 1951a. in the rabbit, rat, and sheep). 



Although Barry (1843) was the first in- 

 vestigator to observe a spermatozoon within 

 the mammalian egg, no detailed description 

 of the process of fertilization appeared until 

 Van Beneden published his observations on 

 the rabbit in 1875. Since then, numerous in- 

 vestigations on the cytology and physiology 

 of fertilization in the mammal have formed 

 a large volume of literature (Van der 

 Stricht, 1910, the bat; Sobotta, 1895, Lams 

 and Doorme, 1908, Gresson, 1948, the 

 mouse; Rubaschkin, 1905, Lams, 1913, the 

 guinea pig; Gregory, 1930, Pincus and Enz- 

 mann, 1932, the rabbit; Tafani, 1889, So- 

 botta and Burckhard, 1910, Kirkham and 

 Burr, 1913, Huber, 1915, Kremer, 1924, Gil- 

 christ and Pincus, 1932, MacDonald and 

 Long, 1934, Austin, 1951a, b, Blandau and 

 Odor, 1952, Austin and Bishop, 1957, the 

 rat; Van der Stricht, 1910, Hill and Tribe, 

 1924, the cat; Mainland, 1930, the ferret; 

 Van der Stricht, 1923, the dog; Pearson and 

 Enders, 1943, the fox; Wright, 1948, the 

 weasel; Hamilton and Laing, 1946, Piykia- 

 nen, 1958, the cow; Amoroso, Griffiths and 

 Hamilton, 1942, the goat; and others). The 

 specific point of emphasis and the degree of 

 completeness of these studies vary widely 

 and in a number of instances only discontin- 

 uous and isolated stages were observed and 

 reported. 



Certain of the many changes occurring 

 during the process of sperm penetration and 

 fertilization can be studied best in fixed 

 material properly sectioned and stained. 

 Many features, however, can be observed 

 most clearly only in the living egg. Obvi- 

 ously one way of studying fertilization phe- 

 nomena is to look at them. But microscopic 

 observations on the living egg even with 

 the newer phase-contrast objectives and 

 other techniques have been disappointing to 

 many because of the problems in establish- 

 ing and maintaining an environment in 

 which the processes can take place. There is 

 such an array of observations of sperm pen- 

 etration and fertilization in the inverte- 

 brates that there has been a tendency to 

 translate these observations directly to the 

 mammalian egg. It is becoming increasingly 

 clear that there is not necessarily a common 

 denominator for these vital processes and 

 that they vary widely. The interesting dif- 

 ferences in the shape of the heads of sper- 



