GERM CELLS IN THE ARTHROPODA 113 
laid in this manner. Gravity apparently has no 
influence upon the development, since eggs in a state 
of nature occupy all positions with respect to 
this factor without becoming altered in any way. 
Only one case has come to the writer’s attention 
of an influence of gravity in insect development — 
the eggs of the water beetle, Hydrophilus atterimus, 
Fic. 35.— A diagramatic drawing of Calligrapha bigsbyana clinging to 
the under side of 1 willow leaf and showing the orientation of the 
egg in the ovarian tubule and after deposition. a@= anterior; d= 
dorsal; p=posterior; r=right side; 2 =place where egg was 
marked with India ink as means of orientation after removal from 
leaf. 
according to Megusar (1906), develop abnormally if 
the cocoon in which they are laid is inverted. 
The events that precede the establishment of the 
primordial germ cells in chrysomelid beetles may be 
described briefly as follows: The egg, when laid 
(Fig. 36, 1), consists of a large central mass of yolk 
globules (y), among which are very fine strands of 
cytoplasm; a thin peripheral layer of cytoplasm, the 
‘““keimhautblastem” of Weismann (khb/), a delicate 
vitelline membrane (v.m.), a chitinous shell, the 
chorion, and a nucleus consisting of the egg nucleus 
I 
