306 Chromosomes in the Spermatogenesis of Anasa Tristis 
The large cross-shaped chromosome can be identified in nearly all the 
photographs, though in many its characteristic shape is more or less 
obscured. In Plate I, Photos. 18 and 21 to 24, the cross form is clearly 
defined, also in Photos. 1, 3, 4, 5, 6, and 8 to 12, Plate IJ. In-many of 
the later stages on this plate the cross form is not so clear but it is well 
defined in Photos. 20 to 26 and in all the cases in which the cross form 
is obscured this chromosome can be identified by its size. At the telo- 
phase of the first spindle and prophase and metaphase of the second 
spindle it can be identified as the largest dyad of each group, its size 
making its identification often possible even as late as the telophase of 
the second spindle. In a recent work on the prophases of the egg of 
Allolobophora we showed that cross-shaped chromosomes could be formed 
by the contraction of two rod-shaped univalents. We described the pro- 
cess as follows: ‘‘ They undoubtedly arise by a simple contraction of a 
bivalent chromosome, 7. e., two rod-shaped univalent chromosomes placed 
end to end. As they contract and are pressed together each splits open 
along the line of the longitudinal furrow, the ends are thus pressed out 
at right angles forming the two arms of the cross.”° The shape of the 
largest chromosome in the group of Photo. 2, Plate II, indicates that 
the cross-shaped chromosome in Anasa may be formed in the same way 
and we also find transitional stages between the two longitudinally spht 
rods and completely formed crosses. In Anasa these transitional stages 
are very common for all the nine chromosomes which often have this 
cross form, and these stages are shown in the early and late prophases and 
metaphases of Plates [and II. There are very few of these preparations, 
which show exactly the same number of well-defined crosses or split 
rods, and the transitional stages between the two forms are too obvious 
to need detailed description. We would accentuate the fact of the 
occurrence of such transitional forms because the omission of such 
forms in other material has been especially noted. 
The large chromosome of Anasa exceptionally shows a form quite dif- 
ferent from the cross, but we believe that in each case its relation to 
the cross form is evident. Such exceptions are seen in Photos. 19 and 20, 
Plate I. These two chromosomes, each the largest of the group, appear 
as two longitudinally split rods placed side by side instead of end to end, 
and thus they seem to foreshadow two longitudinal divisions. We be- 
lieve, however, that they ‘can be interpreted in the hght of the large 
cross-shaped chromosome of Photo. 18. <A further step in closing the 
° Foot and Strobell, o5, p. 219. 
