2i 4 THE EMBRYOLOGY OF THE HONEY BEE 



the ephithelial envelope of the ovary. The cells of this layer are 

 joined together to form an epithelium, but as yet only an imper- 

 fect one, since there are frequent gaps between the cells, and there 

 are also many cells destined to form epithelium, which have not 

 yet become completely differentiated. This is evident in figure 85. 

 At the mesial borders of the ovarian rudiments the ovarian epithe- 

 lium is fairly well formed, and here it is united by a slender point 

 of attachment to the ridge, previously described, which extends 

 along the ventral side of the heart, thus holding the ovaries in 

 place. The component cells of the ovarian rudiments present 

 nothing peculiar in character. Their nuclei are large as compared 

 with those of the adjoining tissues, approaching the size of those 

 of the mid-intestine. As will appear later the cells of the ovarian 

 rudiments are not perceptibly different from the undifferentiated 

 mesoderm cells of earlier stages. 



The ovaries of the honey bee are derived from the genital ridge, 

 which is formed from the visceral wall of the mesodermal tubes 

 in the fifth to the tenth trunk segments inclusive. At Stage X 

 (Fig. 86A) the visceral wall of the mesodermal tubes has already 

 become divided into two layers ; an inner single layer of cells, 

 lying in contact with the yolk, the rudiment of the enteric muscles, 

 or splanchnopleure, and an outer, thicker portion, in which the 

 cells are somewhat irregularly but compactly arranged and which 

 constitutes a part of the visceral layer of the mesoderm. This is 

 the portion destined to form the genital ridge (Fig. 86A, Or). In 

 tranverse section it approximates an ellipse in outline, and in its 

 narrower diameter includes from one to two layers of cells which 

 in appearance do not perceptibly differ from those of the adjacent 

 derivatives of the mesoderm. Even at this early stage the genital 

 ridge has become narrowed at its point of attachment to the neigh- 

 boring structures, the cardioblasts and the splanchnopleure. 



Prior to Stage X, the cells destined to constitute the genital 

 ridge may be seen in active mitotic division and during this period 

 it increases slightly in thickness. Its nuceli seem also to increase 

 slightly in size. At the next stage (XI) the remainder of the vis- 

 ceral layer, now composed of loosely arranged cells, becomes 

 detached from the genital ridge. The outer or somatic wall of 

 the mesoderm is meanwhile becoming differentiated into the rudi- 



