REDUCTION WITHOUT TETRAD-FORMATION 26 1 



seen during the foregoing anaphases. There is therefore no evi- 

 dence of a transverse division. McGregor ('99) describes a nearly 

 similar process in Ainp/iiuina, where the longitudinal division of the 



ABC ^ 



~^\ ' ur^i 



H . J Mi 1' is 



D 



G H 





S(* =*■<** 





y 



Fig. 130. — Maturation in the lamellibranch Zirphcea and in Thalassema. [GRIFFIN.] 



A-E, 7.iiph(Fa ; F-I, Thalassema. 



A. Unfertilized egg, ring-shaped and cross-shaped chromosomes. B. Prophase of first polar 

 mitosis. C. First polar spindle ; double crosses. D. Slightly later stage. E. The double crosses 

 have broken apart (equation-division). G. Ensuing stage; daughter-Vs broken apart at the 

 apex. H. Telophase of first, early prophase of second, division ; limbs of the V's separate but 

 closely opposed. F. Later prophase of second division. /. Second polar spindle in metaphase. 



daughter-V's is seen with the greatest clearness throughout the 

 anaphases. 



The weak point in both the foregoing cases is the fact that all 

 traces of the second longitudinal division are lost during the ensuing 



