Germ Cells and early Embryology. of certain Aphids. 619 
appears only in the growth period and early prophase of the first 
spermatocyte division. In the ova of the same species nucleoli 
appear in the germinal vesicle during the growth period: and dis- 
organize within the nucleoplasm when the polar bodies are formed. 
Degenerating cells are found in the cysts of the different lobes 
of the testes. Seldom more than two cysts in a single lobe are 
affected. These degenerating cells are found at the close of the 
last spermatogonial division and in the prophase of the first sper- 
matocyte division. Degeneration in the first instance is shown by 
a failure of the chromosomes to pass into the granular condition at 
the beginning of the growth period as occurs in the normal cells. 
The chromosomes instead fuse in a common mass, which stains very 
dark. The cytoplasm becomes very clear, more granular and almost 
entirely disappears, leaving a faint ring of cytoplasm around the 
dark chromatin mass (Fig. 111—112). 
In the second instance the chromatin spireme, instead of forming 
the distinct chromosomes, becomes a homogeneous mass (Fig. 113). 
This fused nuclear mass often divides within the cytoplasm and 
gives the appearance of a multinucleate cell (Fig. 114—116). Wırcox, 
1895, in Cicada tibicen and Caloptenus femur-rubrum found that 
degeneration and amitosis as well affected only the spermatogonia. 
2. Ovogenesis. 
a) Parthenogenetic generation. 
The reproductive organs consist of ten follicles in two groups. 
Each follicle is distinctly divided into three parts, end ligament, 
ovariole or end chamber, and oviduct. The oviducts of both sides 
lead to a common uterus. The structure and appearance of a single 
follicle as shown in Pl. 50, Fig. 43, gives the exact relation of the 
three parts or divisions. The end chamber is almost completely 
filled with the nutritive or ovarian glands. Two ova are plainly 
visible at the proximal end of the end chamber. The ova just 
before entering the oviduct are connected with the inner ends cf 
the ovarian glands by the nutritive string. The polar body is 
formed immediately after the egg enters the oviduct (Fig. 43). A 
more advanced stage of an ovum in the early formation of the 
blastoderm is shown in the oviduct. From five to six embryos in 
different stages of development may be found in a single oviduct. 
The ovogonia at the last ovogonial division are composed of a 
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