816 



SPERM, OVA, AND PREGNANCY 



Apparently the ovum plays only a passive 

 role in the process of mucin deposition. The 

 remarkably even distribution of mucin on 

 living eggs or glass beads implies that the 

 oviduct has a specific pattern of muscular 

 contraction so as to rotate the eggs as they 

 move forward. 



If the mucous coat is vitally stained with 

 toluidine blue, one observes a concentric 

 stratification which may indicate an apposi- 

 tional growth as the egg proceeds through 

 the oviduct. Chemically the mucous coat is 

 composed chiefly of strongly acid mucopoly- 

 saccharides. It is readily dissolved by tryp- 

 sin, chymotrypsin, and pepsin. It is not af- 

 fected by hydrochloric acid solutions as 

 strong as 0.1 M but it may be slowly removed 

 by solutions more alkaline than pH 9. A pe- 

 culiar and important proi)erty of the al- 

 buminous coat is that at pH 9 or 10 it be- 

 comes exceedingly sticky. As will be noted 

 later, this may be of importance for the ad- 

 herence of the egg to uterine tissue at the 

 time of implantation. The possible role of 

 the mucous coat in the development of the 

 egg was not realized until the investigations 

 of Boving (1952c) in which certain details 

 of rabbit blastocyst implantation were ob- 

 served directly. A plastic chamber was de- 

 veloped for examining the interior of the 

 pregnant rabbit uterus. It was noted that 

 the mucous coat participates actively in the 

 initial adhesive attachment of the blastocyst 

 to the uterus. Such localized attachment 

 precedes by several days the cellular ad- 

 hesion and invasion of the uterus by the 

 blastocyst. Boving observed further that the 

 adhesion to the uterus is localized in the 

 abembiyonic hemisphere of the blastocyst, 

 probably because it is in this region that an 

 alkaline reaction, produced by secretions of 

 the embryo, enhances the stickiness of the 

 mucous coat. The polar localization of the 

 adhesive attachment of the mucous coat not 

 only provides a mechanism for the initial 

 blastocyst attachment, but also is impor- 

 tant in establishing the orientation of the 

 blastocyst within the uterus (see section on 

 "Spacing and orientation of ova in utero"). 



Boving (1954) observed that still another 

 membrane is deposited on the rabbit egg by 

 secretions of the uterus. The membrane 

 forms a sticky covering that stains meta- 



chromatically in toluidine blue and func- 

 tions as an adhesive attachment during po- 

 sitioning and orientation of the blastocyst 

 in utero. He proposed that the noncellular, 

 adhesive layer be called the "gloiolemma." 



D. THE FIRST MATURATION DIVISION 



Meiotic division is not a phenomenon 

 which is confined entirely to the ova in the 

 preovulatory follicles. It may be encoun- 

 tered in egg cells in the latter part of em- 

 bryonic development, in immature follicles 

 undergoing atresia, and in ovaries stimu- 

 lated excessively by the animal's own pi- 

 tuitary hormones, or by pituitary hormone 

 preparations which have been injected 

 (Evans and Swezy, 1931; Guthrie and Jef- 

 fers, 1938; Dempsey, 1939; Witschi, 1948). 



Fairly complete descriptions of the vari- 

 ous stages in the formation of the first po- 

 lar body and second maturation spindles 

 are available for a number of mammals 

 (Hartman and Corner, 1941, the macaque; 

 Hoadlcy and Simons, 1928, Hamilton, 1944, 

 and Rock and Hertig, 1944, the human; 

 Kirkham and Burr, 1913, Blandau, 1945, 

 Odor, 1955, the rat; Long and Mark, 1911, 

 the mouse; Moore, 1908, the guinea pig; 

 Langley, 1911, the cat; Van Beneden, 1875, 

 Pincus and Enzmann, 1935, the rabbit; Rob- 

 inson, 1918, the ferret). 



Specific data on the temporal relationship 

 between ovulation and the first maturation 

 division are available primarily for the rab- 

 bit (Pincus and Enzmann, 1935-1937), 

 guinea pig (Myers, Young and Demi-)sey, 

 1936), cat (Dawson and Friedgood, 1940), 

 rat (Odor, 1955), and mouse (Edwards and 

 Gates, 1959). 



Tlie rabl)it is an animal particularly 

 suited for studies of maturation phenomena 

 because it ovulates regularly between 9 and 

 10 hours after copulation. The first evidence 

 of change in the nucleus of a ripe ovum may 

 be seen 2 hours after copulation. At this 

 time the nuclear membrane is intact but 

 tetrad formation is in evidence. Four hours 

 after copulation the nuclear membrane has 

 disappeared and the first polar spindle, with 

 tetrads located on the metaphase plate, oc- 

 cupies a paratangential position near the 

 periphery of the ooplasm. Abstriction of the 

 first polar body is completed about 8 hours 



