32 Hyhridizntinn of Echinoids. 



lagging chromosomes which will be at the line of division of the cell 

 and which will lie at the position of the Zwischenkorper. 



21 



a 22 



Fig. 21, a and b, Cidaris 9 X Tripneustesd^. Two V's and book, 25-34. 

 Fig. 22, a and h, Cidaris 9 X Tripneustesif. Three V's, 29-28. 



'('''fAi ",»|i> 



I'^/t/ 



«. 23 ^' <^ 534 ^, 



/ If'/ "•'/// // // Z//'^ 



/~t 



/ 



Fio. 23, a and b, Cidans 9 X Tripneustes d" . Two V's and hook, 22-26. , • , , , 



Fig. 24, o and b, Cidaris 9 X Tripneustesd'. Early anaphase; the position and width of 



the chromosomes in b give clear evidence that these are merely sections of tho.se 



shown in a. Two V's, 



Elimination of Chromosomes. 



In 1912 I summarized the facts regarding retention or elimination 

 of chromosomes in cross-activated Echinoid eggs as follows: 



(1) Elimination of no chromosomes and dominance of one species over the other 



with respect to the character of the skeleton. 



(2) Elimination of part of the chromosomes and dominance of one species over the 



other with respect to the character of the skeleton. 



(3) Elimination of no chromosomes and skeleton of intermediate character. 



(4) Elimination of part of the chromosomes and skeleton of intermediate character. 



(5) Elimination of part of both maternal and paternal chromosomes and inhibition 



of development. 



