454 Gregory . — Spore- Formation in Leptosporangiate Ferns . 
by the distribution of the tetrads shown by Rlickert in his Figs. 25 
( Heterocope ) and 34 (Diaptomus). 
The question therefore suggests itself whether each tetrad may not 
consist of two univalent chromosomes, one of paternal, the other of 
maternal origin. This view agrees with that which is generally accepted 
of the significance of the bivalent chromosomes, but leaves unexplained 
for the present the later separation of the tetrads into groups. If it is 
correct, the movements of the chromosomes described by Hacker will 
Fig. 43. Diagrams of the reduction-division in Cyclops. 
The chromosomes are white or shaded to indicate their suggested origin from the two parents. 
A, from Hacker. B-E, the interpretation suggested in the text. A and B, the oocyte. C, the 
formation of the first polar body indicating the distribution of the chromatin which would follow 
from B. The orientation assumed by the chromosomes in the next stage may be as in Di, as in the 
converse of Di, or as in Dn, with the result that the egg may contain chromatin from one parent only 
(El and its converse), or any of the combinations of paternal and maternal chromatin (Eli), which 
become possible with a larger number of chromosomes than the four represented in the diagrams. 
provide for any arrangement of the paternal and maternal chromatin in 
the gametes, since the different relative positions assumed by the chromo- 
somes in the c secundaren Keimblaschen 1 ’ permits either the paternal or 
the maternal element to be turned indifferently towards either pole. (See 
Fig. 43 in text.) 
The regularity observed by Hacker in the movements of the chromo- 
somes at the reduction-division may perhaps be an indication, in a limited 
degree s of a more comprehensive symmetrical design extending throughout 
the nuclear divisions which provide for the production of the different 
types of gametes in Mendelian hybrids. c It is impossible to be presented 
with the fact that in Mendelian cases the cross-bred produces on an 
1 See Hacker (’ 03 ), PI. 19, Figs. 36-38. 
