Gregory . — Spore- Formation in L eptosporangiate Ferns . 453 
chromosomes of the two groups pass between one another ‘ in einer ganz 
gesetzmassigen Quadrillen-ahnlichen Ordnung 1 / with the result that f die 
Eizelle in gleichmassiger Mischung grossvaterliche und grossmtitterliche 
Elemente erhalt 2 .’ 
These later results apparently indicate that in Cyclops the gametes 
always contain chromosomes derived from both parents. 
The view adopted here of the significance of the reduction-division 
appears then to be open to the objection that no provision is made for the 
production, among the different kinds of gametes, of a certain number bear- 
ing Mendelian characters derived exclusively from one parent. 
This objection involves the assumption, which is not at present justified 
by evidence, that each pair of chromosomes corresponds with a pair of 
allelomorphic characters, and that the correspondence is independent of 
any effect due to the presence or absence of other chromosomes 3 . 
There is, however, another possible interpretation of the phenomena 
observed in Cyclops . Hacker supposes that of the two groups of tetrads 
ab cd ef gh ik lm 
ab cd ef gh ik lm 
the series -7, — , 
no pq 
no pq 
ab cd 
ab' cd 
no pq 
the series — , — 
710 pq 
rs 
rs 
tu vw xy 
tu vw xy 
originates from one parent, 
from the other. 
If this is so, the plane of separation between the paternal and maternal 
groups is now at right angles to the position it occupied in the earlier 
stages 4 . 
In Cyclops strenuus , Heterocope robusta and Diaptomus gracilis , the 
tetrads are at first evenly distributed throughout the nuclear cavity of 
the oocyte 6 . In the first-mentioned form there appears at a later stage 
a distinct tendency towards the separation of the tetrads into two groups 6 . 
In the other forms this is less marked, but may perhaps be indicated 
1 Hacker, 1 . c., p. 342. 2 Ibid., p. 374. 
3 The degree to which the analysis of the nucleus has been carried (Boveri, ’ 02 ) only admits 
of the application of the conclusions to combinations of chromosomes, of which a large number are 
possible even under the conditions which obtain in Cyclops , if Hacker’s suggestion is correct. 
Further the characters exhibited by certain heterozygotes appear to be only explicable as corresponding 
with a combination of chromosomes. To use a physical analogy, a combination of chromosomes 
may be compared to a chemical compound as distinct from a mechanical mixture. But in citing 
heterozygotes as an instance of the effect of a combination of chromosomes it must not be forgotten 
that we are dealing with a zygote-nucleus and not with a reduced one. 
4 See Hacker, 1 . c., Figs. 28, 29 (. Diaptomus denticornis') ; Riickert (’ 95 ), Figs. 1-3, 6, 7 ( Cyclops 
strenuus ). 5 Riickert (’ 94 ). 6 1 . c., p. 303, and Figs. 15 and 20. 
