490 
Katharine Foot and E. C. StrobelJ 
spermatocytes of servus. In photos 10, 11 and 12 the X Y cliromo- 
somes of servus are side by side and it is obvious that the difference 
in the size of these two chroniosomes is qnite as marked in servus as 
in variolarius. 
The second spermatocyte chi'oniosonies of variolarius are demonstra- 
ted in photos 5 to 8 and those of servus in photos 13 to 15. These photos 
demonstrate that the X Y chroniosomes of both species separate in the 
second division, the two going to opposite poles. A late telophase of 
this division is shovn for variolarius in photo 9. This stage is frequently 
met in both variolarius and servus and also in the Fi and F 2 genera- 
tions. 
Comparative. 
A comparison of the above mentioned 3 stages of variolarius and 
servus with the saine stages in the Fi and Fg generations will show 
that the chroniosomes in the two parent species and in the two hybrid 
generations are apparently ahke in their form and their behaviour — they 
have no differential features that are constantly present and therefore 
their morphological individiiality caniiot be put to the test of experi- 
mental breeding. The first metaphase chroniosomes of variolarius are 
shown in photos 1 to 4, those of servus in photos 10 to 12, those of the 
Fl hybrids in photos 16 and 17, and those of the F 2 hybrids in photos 24 
to 27 (photo 28 shows a fhst telophase). 
The second metaphase chi’oniosonies of variolarius are sliowii in 
photos 5 to 8, those of servus in photos 13 to 15, those of the F i hybrids 
in photos 18 to 23 and those of the F 2 hybrids in photos 29 and 30. 
A late telophase of the second division is shown for variolarius in photo 9, 
and photo 31 shows the sanie stage in an F 2 hybrid. 
A comparative study of these photographs falls to reveal any dif- 
ferential character in the chi'oniosonies that is sufficiently marked and 
constant to be of gcnetic value as a fest of the individiiality of the chro- 
mosonies — they nierely support AYilsox’s (’06), and later Montgo:mery’s 
T06) observations as to the behaviour of theXA^ chroniosomes in mno- 
larius and servus. 
The visible morphological difference in the sperniatids resulting froni 
the second division (photos 9 and 31) is one example of the evidence dis- 
covered in the insects that there are two types of sperniatozoa differing 
in the form or nuniber of their chroniosomes, this discovery having raised 
the important question whether a morphological difference in their cliro- 
niosonies involves a functional difference in heredity. This question has 
