68 W. JS. Kirkham — Maturation of the E(j(j of the White Mouse. 



and witnessed the formation of the second polar body (he found 

 two associated with only one-fifth of the eggs). He also saw sper- 

 matozoa entering the substance of the egg, the two pronuclei, the 

 first cleavage s]iindle, and tlie principal later cleavage stages. 



Sobotta studied the egg of the mouse in great detail, from the end 

 of the spireme through the cleavage stages. He found two polar 

 bodies accompanying only one-tenth of the fertilized eggs, and 

 assumed the suppression of the first polar spindle in the oth9r nine- 

 tenths of the eggs matured. When the first polar body did occur, 

 he observed that it was extruded within the ovary. Further refer- 

 ences to Sobotta's valuable work will be given in connection with 

 the discussion of the results of the writer's personal investigations, 



Gerlach has taken some preparations made at least as early as 

 1890, before the discovery of iron haematoxylin, and, after study- 

 ing them has revived Tafani's theory that the presence of the single 

 polar body, which he finds with three-quarters of the fertilized eggs, 

 is due to the suppression of the second polar body, the second polar 

 spindle degenerating within those eggs which are fertilized a com- 

 paratively long time after leaving the ovary. 



Henneguy ('94) observed in the rat degenerating ovarian eggs 

 which had extruded the first. polar body, — an observation confirmed 

 by the writer, 



Assheton ('94) has reinvestigated the early stages of development 

 of the rabbit, and seen stages extending from the union of the 

 pronuclei through cleavage. 



Hubrecht ('96) succeeded in getting some eggs of an insectivore, 

 Tupaja javanica, and noted the two pronuclei, a two-celled stage, 

 and the ijrincipal later cleavage stages. He found two polar bodies. 

 This same investigator (:02) has the honor of being the only man 

 who obtained the mature eggs of any primate. He both describes 

 and figures from Tarsias spectrum an egg with first polar body and 

 second polar spindle, three eggs with male and female pronuclei, 

 two of which show two polar bodies, as well as two-, four-, eight-, 

 and sixteen-celled stages, besides the principal later cleavages. 



Van der Stricht (:0l) finds in the eggs of a bat, Vexperugo noetula, 

 that the first polar body is extruded within the ovary, while the 

 second is formed only after the ovum has been discharged into the 

 Fallopian tube. In his later papers (:05, :o6) he notes a distinction 

 in the form of chromosomes in the first and second polar spindles, 

 and states that the first maturation spindle commonly appears in 

 February or JNIarch, sometimes not until April, depending upon the 

 temperature. Ovulation occurs some days or weeks later. Two 



