BIOLOGY OF EGGS AND IMPLANTATION 



857 



epithelium of the antimesometrial border of 

 the cornu. In 1883 von Spee described an 

 increase in the size and number of the 

 abembryonal pole cells of the guinea pig 

 shortly before implantation of the blasto- 

 cyst and gave an account of the pseudo- 

 l)odia-like processes of these cells penetrat- 

 ing the zona. These processes were regarded 

 by other investigators as fixation artifacts 

 or "as of the nature of a secretion" (Sansom 

 and Hill, 1931). Recently, the early im- 

 l)lantation of the guinea pig has been 

 reinvestigated and the observations of 

 van Spee have been confirmed (Blandau, 

 1949b). It is remarkable that there 

 should be so little change in the zona 

 of the guinea pig egg during its 3 day 

 sojourn in the cornu. The blastocyst com- 

 pletely fills the perivitelline sjiace and the 

 abembryonal pole cells comprise but a single 



layer (Fig. 14.19). Within a few hours be- 

 fore the ovum attaches itself to the uterine 

 epithelium, the abembryonal pole cells pro- 

 liferate to form the implantation cone. The 

 trophoblast cells lying next to the zona 

 send numerous slender protoplasmic proc- 

 esses through it (Fig. 14.20) until the abem- 

 bryonal pole is riddled with them. The cyto- 

 plasmic extensions increase rapidly in size 

 and may extend as bulbous expansions of 

 varying shape for some distance beyond 

 the zona pellucida (Fig. 14.21). It is only 

 in the region where the zona is perforated 

 by the extension of the abembryonal pole 

 cells that it gradually becomes thinner and 

 disappears. The remainder of the zona pel- 

 lucida has been observed in vitro to slough 

 off from the attaching blastocyst, much as 

 a grape skin is removed from the flesh of 

 the grape. Attachment cones have been de- 



FiG. 14.20. AiiiK-aiaiicc of li\iiig guinea pig l)la.'<tiicysi api>r()xiiiiaii'l\- oiic hour before at- 

 tachment of the abembryonal pole to the endometrium. Note the increase in the number of 

 the abembryonal pole cells and the cytoplasmic extensions of these cells through the zona 

 pellucida. X900. 



