DEVELOPMENT PRIOR TO LAYING 



37 



The entrance of several spermatozoa appears to be character- 

 istic of vertebrates with large ova; thus for instance, it has been 

 described in selachii, some amphibia, reptiles, and birds. Such 

 a condition is known as polyspermy; it is normal in the forms 

 mentioned, but occurs only under abnormal conditions in the 





Kc--'"v^^a.";.\...-. -J . 







fete* •.:,■ 



pfe::.,:: .;::. 



3g:"-..v.-,-'. ■..■.;••; •■•■••;."■ • 

 '?K-'i."'-''-^.".".vi--'-v'-'.':'. ■'.■■•■.'•■■-■■• .: 





- • •'''','}y»;i'""-'-V'^*^'^'" 



.■.•■.■ .•■H»;;.-.-..-.iA>;-; 



p.r 



JV 



■.■"v-f;';.-;-"-:rJi ^Y~' _ 



Fig. 14. — Horizontal section of the germinal disc of a pig- 

 eon's ovum immediately after ovulation, x 125. (After 

 Harper.) 



N., Nucleus, probably first maturation spindle, p. r., 

 Polar ring. Sp. N., Sperm nuclei. 



m. 



.V'"-:-'":'--4-'>?*va 



>f--;':- 



-.-■.•■•■.,•". ■•.•■-,..— .■-. •■■;--.:-''ftdsT| 



;.^.v •■;■■■■ •'•■••x•;:•:-^:■>i::V^^'iv•^:i!i^^^ 





Fig. 15. — Vertical section of the pigeon's egg showing germ nuclei 

 (pronuclei) in the center of the disc, x 2000. 10.40 p.m. (After 

 Harper.) 



