GERM CELLS IN THE ARTHROPODA 111 
Hegner (1908, 1909a, 1909b, 191la, 19116, 1914a), 
and Wieman (1910a, 1910b) will be referred to in 
the following paragraphs. 
Wheeler (1889) figured several primordial germ 
cells in an egg of Leptinotarsa with a segmented germ 
band and _ suspected 
their true nature, but 
did not discover them 
in earlier stages. Le- 
caillon (1898) de- 
scribed the pole-cells 
in several chrysomelid 
beetles, but did not 
make out any of the 
details concerning 
their origin, structure, 
and migrations. 
Within the last 
seven years the writer 
has devoted a consid- Fra. 34. — Calliphora. A. Longitudi- 
$ ‘ nal section through posterior end of 
erable portion of his freshly laid egg, showing ‘ Dotter- 
time to morphological platte (Dpl). B. Longitudinal sec- 
d . tion through posterior end of egg at 
an experimen tal time of blastoderm formation, showing 
studies of the eggs of pian Pe ay els 
beetles, particularly 
Calligrapha bigsbyana, C. multipunctata, C. lunata, 
and Leptinotarsa decemlineata. The eggs of these 
species are peculiarly favorable for study, since they 
are definitely oriented in the body of the mother 
and various surfaces can be recognized in the newly 
laid egg: they can be placed under the most severe 
