412 A. J. NICHOLSON 
disconnected fragments of the branching nucleus can be distin- 
guished in the yolk-mass, even in eggs which have been laid. 
‘The only other protoplasmic structure visible is a small mass 
of granular protoplasm situated about a quarter of the length 
of the egg from the anterior pole and in the centre of the yolk- 
mass. This appears to be the remains of the chromatin residue, 
but before the egg is laid no nuclear structure can be distin- 
guished in it. A short time after oviposition, however, this 
mass 1s found to contain minute chromosomes. 
DIFFERENTIATION OF GERM-CELLS AND THE First Prriop 
OF GROWTH OF THE EGG-FOLLICLES. 
The growth of the egg-follicle falls naturally into two periods. 
The first period is from the time when the follicle is separated 
off from the end chamber up to the formation of the ‘ resting 
stage’. Growth is arrested at this point and only recommences 
after the insect has had a good meal of blood, when the follicle 
enters upon the second period of growth, which culminates in 
the formation of the mature egg. In the second and later 
generations of eggs, however, the two periods run concurrently, 
i.e. while the primary follicles are undergoing the second period 
of growth the secondary follicles are undergoing the first, 
and when the former have formed the mature egg the latter 
have reached the ‘ resting stage’. 
If an end chamber in an early stage of development be 
examined it will be found to consist of a central mass containing 
comparatively large nuclei surrounded by a layer in which 
smaller nuclei are found scattered somewhat irregularly. 
Cell divisions cannot be distinguished and the mass is probably 
a syncytium (fig. 24). The larger central nuclei are those of 
the oogonia and oocytes, and the smaller peripheral ones give 
rise to the follicular epithelium. 
The nuclei of the oogonia vary considerably in appearance 
even in the same mass, but in the earlier stages of the end 
chamber I have been unable definitely to separate the true 
ooeyte from the nurse-cells. Occasionally mitotic figures are 
found in the central mass (fig. 31). This is no doubt the stage 
