82 ir. ]>. Kirkhitm — J/dturation of the Egg of the White Mouse. 



3. 'J'wclve masses of cliromatin are cast out willi the first ])olar 

 body, and a like iiiunber remain in the e^^g. 



4. Tliere is a sharp distinction in form between tlie cliromosomes 

 of the first and those of the second polar spindle. 



5. Before fertilization, every Qgg in the Fallopian tube possesses a 

 second polar spindle. 



(i. The zona ])ellucida, which is (juite distinct, ma}' persist, undi- 

 minished, through tlie early cleavage stages. In most cases the first 

 ])olar body escapes- from it during the process of ovulation, so that 

 tlie majority f>i eggs after fertilization possess the second jiolar 

 bod}' only. 



7. During tlie sjtriiig months ovulation usuall}^ occurs every 21 

 days within a few hours after parturition, and independent of copu- 

 lation. 



8. The numl)er of univalent chromosomes in the second polar 

 spindle is 24. 



n. The second polar body is formed only after the ogg has been 

 fertilized. 



10. The first and second polar bodies differ greatl}^ in chromatin 

 content, so that they are easily distinguishable. The}' also differ in 

 size, and usually in shape. 



1 1. At least the greater part of the sperm tail, if not the whole, 

 enters the egg at the time of fertilization. 



1 2. Since the egg of the mouse forms two polar bodies, its 

 maturation processes are in accord with those of the majority of 

 metazoon eggs. 



IV. BIBLIOGRAPHY. 

 Assheton, R. 



'94. A reinvestigation into the early stages of development of the rabbit. 

 Quart. Jouni. Mic. Sc, Vol. 37. 

 Baev, K. E. von. 



'28. Uber Entwicklmigsgeschichte der Thiei'e-Beobachtung und Reflexion. 



I. Kouigsberg. 

 '37. II. Konigsberg. 

 Barry, M. 



'38. Researches in Embryology. First Series. Phil. Trans. R. Soc. 



Loudon. 

 '39. Second Series. Phil. Trans. R. Soc. London. 

 Belloaci, O. 



'85, Del fuso direzionale e della formazione di un globulo polare nell' 

 ovialo ovarico di alcvmi mammiferi. Atti R. Accad. Line. (4) 

 Rendicont., Vol. 1, Fasc. 9. 



