MATURATION OF PARTHENOGENETIC EGGS 



203 



same fact in the butterfly Liparis ('89) a fact which seemed to con- 

 tradict Boveri's hypothesis. Brauer's beautiful researches resolved 

 the contradiction by showing that there are two types of parthenogene- 

 sis which may occur in the same animal. In the one case Boveri's 



-c^m^ A 



O 



o 



> 



D 



E 



Fig. 100. First type of maturation in the parthenogenetic egg of Artemia. [BRAUER.] 

 A. The first polar spindle; the equatorial plate contains 84 tetrads. B. C. Formation of the 

 first polar body ; 84 dyads remain in the egg and these give rise to the egg-nucleus, shown in D. 

 F. Appearance of the egg-centrosome and aster. E. G. Division of the aster and formation 

 of the cleavage-figure; the equatorial plate consists of 84 apparently single but in reality bivalent 

 chromosomes. 



conception is exactly realized, while the other is easily brought into 

 relation with it. 



(a) In both modes typical tetrads are formed in the germ-nucleus 

 to the number of eighty-four. In the first and more frequent case 

 (Fig. 100) but one polar body is formed, which removes eighty-four 

 dyads, leaving eighty-four in the egg. There may be an abortive 

 attempt to form a second polar spindle, but no division results, and 



