CHANGES IN THE OVARY 127 



It is commonly believed that the chromatin material is the 

 substance which has the potentialities of development, and which 

 plays the principal part in perpetuating the hereditary structure 

 and qualities of the particular animal or plant, but there is no real 

 proof that this is effected by them exclusively (see p. 204). 



The maturation phenomena may take place within the ovary 

 prior to the discharge of the egg, or they may be postponed until 

 after ovulation has occurred. In the rabbit, as has been shown 

 already, the polar bodies are formed while the ovum is still in the 

 ovary, and the same is believed to be the case in man. 1 



In the case of the mouse, Sobotta 2 came to the conclusion that 

 the first polar spindle is suppressed, and that the second polar body 

 might be formed during the passage of the ovum down the 

 Fallopian tube. Gerlach 3 describes the second polar body as being 

 in some instances suppressed after the entry of the spermatozoon in 

 fertilisation, the second polar spindle degenerating within the egg. 

 Kirkham, 4 however, states that the maturation of the mouse's 

 ovum is in no way exceptional, the process involving the formation 

 of two polar bodies as in most other animals. The first polar body 

 is extruded in the ovary, while the second is given off in the 

 Fallopian tube immediately after fertilisation by a spermatozoon. 6 

 Rubaschkin 6 has shown that the maturation processes in the 

 guinea-pig are similar. In both the guinea-pig and the mouse, ova 

 which are retained in the ovary, and also those which are discharged 

 and fail to become fertilised, undergo degeneration with the second 

 polar spindle within them. 



The maturation phenomena in the bat ( Vesperugo noctula) have 

 been investigated by van der Stricht, who has published a series of 



"Animal Parthenogenesis," /Science Progress, vol. iii., (July) 1908 ; and Cytology, 

 Cambridge, 1920. These works contain further references. 



1 Thomson (A.), loc. cit., 1919. 



2 Sobotta, " Die Befruchtung und Furchung des Eies der Maus," Arch. f. 

 Mikr. Anat., vol. xlv., 1895. 



3 Gerlach, Ueber die Bildung der Richtungskorper bei Mu& muswdus, 

 Wiesbaden, 1906. 



* Kirkham, "The Maturation of the Mouse Egg," Biol. Bull., vol. xii., 

 1907; and "The Maturation of the Egg of the White Mouse," Trans. Con- 

 necticut Acad. Arts and Sciences, vol. xiii., 1907. 



5 Sobotta (" Die Bildung der Richtungskorper bei der Maus," Anat. Hefte, 

 vol. xxxv., 1907), in a further paper, expresses himself doubtful as to whether 

 two polar bodies are really discharged in all cases in the maturation process 

 of the mouse's ovum. His own observations lead him to conclude that two 

 polar bodies are discharged in not more than one-fifth of the total number 

 of maturations, only one polar body being formed in the great majority of 

 cases. Lams and Doorme ("Nouvelles Recherches sur la Maturation et la 

 Fecondation de 1'CEuf des Mammiferes," Arch, de Biol., vol. xxiii., 1907) state 

 that they found two polar bodies expelled in forty-four cases out of forty-eight, 

 the first being always smaller than the second. 



6 Rubaschkin, " Ueber die Reif ungs- und Befruchtungsprocesse des Meer- 

 schweincheneies," Anat. Hefte, vol. xxix., 1905. 



