Germ Cells and early Embryology of certain Aphids. 623 
liferate very rapidly and form the end ligament. Those at the 
proximal end also proliferate very rapidly and form the oviduet. 
The proliferation in the formation of the oviduct continues until it 
meets the invagination of the hypodermis which forms the vagina. 
The more interior cells of the cluster that do not contribute to the 
formation of the end ligament.and oviduct cease to divide, become 
glandular and form the ovarian glands of the end chamber (Fig. 29). 
These glandular cells in their earlier development are often 
mistaken for the true ova. The end chamber is almost completely 
filled with these ovarian glands. The peripheral cytoplasm of these 
glandular cells becomes vacuolated as growth proceeds. In later 
development the inner ends of these ovarian glands become connected 
with the nutritive string (Fig. 30). The condition of the follicle at 
birth in Fig. 30 represents the ovarian glands as almost completely 
developed. The follicular walls of the end chamber now become 
lenticular, except at the extreme proximal end where some of the 
follicular cells continue to divide and give rise to the ova. Three 
ova are plainly visible in the lower end of the end chamber. 
The cytoplasm of the nutritive string has begun to surround the 
ovum in the center of the other two. The ovum becomes united 
with the cytoplasm of the nutritive string immediately after 
growth begins. Very rarely does more than one ovum become 
connected with the nutritive string at a time. Ova that fail 
to unite with the nutritive string to not develop, but gradually 
become disorganized within the cytoplasmic contents of the end 
chamber. Fig. 31 shows a cross section of an ovum at the time 
of entering the oviduct at the extreme base of the end chamber. 
The condition of the follicular wall is plainly represented. Some 
of the follicular nuclei are in mitoses which give rise to the ova. 
These potential germ cells continue to pass from the follicular 
wall into the basal cavity of the end chamber, until the aphid is 
almost completely grown, or as found in some instances until the 
beginning of the deposition of the winter eggs. Less than half of 
the ova that enter the end chamber develop. | 
The ovarian glands reach their adult condition at the beginning 
of the period of deposition as shown in Fig. 32. The follicular 
nuclei at the base of the end chamber no longer divide, and the 
ova cease to be formed. Fig. 32 shows the exact relation of the 
Ovarian glands, nutritive string and ovum. The true condition of 
the follicle at the end of deposition of the winter eggs is represented 
