502 TEXT-BOOK OF ENTOMOLOGY 



"The lowest egg in an ovarian tube is nearly or altogether of the full size ; 

 it is of elongate-oval figure, and slightly curved, the convexity being turned 

 towards the uterus. It is filled with a clear albuminous fluid, which mainly 

 consists of yolk. The chorion now forms a transparent yellowish capsule, which, 

 under the microscope, appears to be divided up into very many polygonal areas, 

 defined by rows of fine dots. These areas probably correspond to as many 

 follicular cells." (Brandt, from Miall and Denny.) 



In the second type, i.e. those egg-tubes with nutritive cells, there are two 

 kinds. In the first the egg-chambers and yolk- or nutritive chambers alternate, 

 each of the latter containing one or more nutritive cells, which serve for 

 the nourishment of the ripening egg contained in the neighboring chamber. 

 "The egg- and yolk-chambers may be distinctly separated externally by con- 

 strictions (Hyinenoptera and many Coleoptera), or one nutritive and one 

 egg-chamber may lie in each section of the ovarian tube, which is exter- 

 nally visible as a swelling (Lepidoptera, Diptera)." 



In the second kind with nutritive cells, the actual tube consists (Fig. 474, <7) 

 of ovarian chambers only ; the nutritive cells here remain massed together in 

 the large terminal chamber. The single egg in the tube is united with the 

 terminal chamber by connective strands (d. s.), which convey the nutritive 

 material to the eggs. (Lang.) 



Egg-cells, nutritive cells, and the cells of the follicle-epithelium (epithelium of 

 the chambers of the ovarian tubes) are, says Lang, according to their origin, 

 similar elements, like the egg and yolk-cells of the flat worms (Platodes); divi- 

 sion of labor leads to their later differentiation. Only a few of the numerous 

 egg-germs develop into eggs, the rest serving as envelopes and as food for these few. 



Korschelt considers that all the chief elements of the egg-tubes, viz. egg, 

 nutritive, and epithelial cells, arise by a direct transformation of the elements of 

 the terminal chamber, and that the last may be traced to the indifferent elements 

 of the terminal thread, the elements in question originating from the nuclear 

 elements by a breaking down of the syncytium (or masses of protoplasm with 

 nuclei scattered through it) composing it (Fig. 475). 



The latest work is that of Wielowiejski (Zoologische Anzeiger, ix, 1886, p. 

 132), whose observations are based on a study of the ovarian tubes and the grow- 

 ing eggs of the Hemiptera (Pyrrhocoris), the Coleoptera (Telephorus, Saperda, 

 Cetonia and Melolontha, Carabidse, and Hydradephaga), etc. 



Wielowiejski divides the ovai'ies of insects into three groups : 



1. Comprising such ovaries in the ends of whose egg-tubes (terminal filament) 

 the embryonal cells in the early stages are accumulated, and are transformed 

 into egg-, yolk-, and epithelial cells respectively. (Ovaries of Orthoptera, geo- 

 dephagous and hydradephagous Coleoptera, Lepidoptera, Diptera, and Hyinen- 

 optera). 



2. Comprising ovaries whose ends above the egg-cells and egg-germs (Eian- 

 lagen) possess throughout life a more or less voluminous solid accumulation of 

 cells (terminal chamber), but which stand in no close relation with the first. 



FIG. 474. Various types of ovarian tubes, diagrammatic: A, ovarian tube without nutritive 

 cells. , ejrjjf-tube with alternating nutritive and ejrfr-eonipartments. <\ ovarian tubes in which 

 the terminal chamber (ek) is developed into a nutritive chamber, with which the developing 

 efrtfs remain connected by means of threads (V/.x) ; ej\ terminal tilamciits: tfii. e-ri: compartment- or 

 chambers; f'r, follicle epithelium : <lf. yolk-chambers. After Lanir < r from Clan ). 



FIG. 475. Upper portion of the ovary in Forflcula, showinsr esrirs and nurse-cells; below, a 



Eortlon of the nearly ripe e<r^ (,-) M.o\\inir aentoplaam-SpberM and irerminal vesicle (</<. Above it 

 es the nurse-cell (n), with its enormous branehinjr nucleus. Two successively younirer stages of 

 egg and nurse-cell are shown above. After Korschelt. from Wilson. 



FIG. 476. J. ovarian eL'tr of a butterlly (Vanessa), surrounded by its follicle; above are the 

 nurse-cells ( <.). witli branching nuclei : ;/.)-. germinal vesicle. />'. cj:<: of Dyticus. livinp : the ei:^ 

 (o.r.) lies between two groups of nutritive cells ; the germinal vesicle sends amoeboid processes into 

 the dark mass of food-granules. After Korschelt, from Wilson. 



