THE EMBRYOLOGY OF THE HONEY BEE 259 



duct is formed by them for the silk glands, opening near the tip 

 of the labrum. 



The oenocytes are produced by immigration of cells from local- 

 ized areas of the lateral ectoderm. There are eight pairs of these 

 situated on the first eight abdominal segments, in line with the 

 openings of the tracheal invaginations. 



The mesoderm, soon after its formation, becomes differentiated 

 laterally into two layers, an outer somatic and an inner splanch- 

 nic layer, while along the ventral mid-line it remains single lay- 

 ered. Separate coelomic sacs are not present, the somatic and 

 splanchnic layers of each side being continuous longitudinally 

 throughout the trunk. At the lateral margins of the mesoderm 

 the two layers are continuous and in this region are composed of 

 long columnar cells. The fate of the various parts of the 

 mesoderm is as follows : The median single-layered section 

 breaks up into the rounded blood cells. The somatic layer forms 

 the trunk muscles, both longitudinal and oblique, the pericardial 

 fat cells, and the dorsal diaphragm, including the pericardial cells. 

 The splanchnic layer sends off from its dorsal border a mesial 

 layer which forms the muscular layer of the mid-intestine. The 

 remainder of this layer is principally concerned in the formation 

 of the two main divisions of the fat body. The heart is formed 

 by the union, along the dorsal mid-line, of two rows of cells, the 

 cardioblasts, which are derived from the angle formed by the 

 union of the somatic and splanchnic layers at the lateral margins 

 of the mesoderm. A mass of mesoderm cells, forming the 

 anterior end of the mesoderm, and evidently belonging to the 

 primary head segment, closely surrounds the stomodaeum at its 

 appearance, and later forms the muscular layer of the fore in 1 

 testine. A similar mass at the posterior end of the embryo forms 

 the muscular layer of the hind-intestine. 



The ovaries are apparently derived from the cells constituting 

 the genital ridges ; these cells are not visually distinguishable from 

 undifferentiated mesoderm cells. The two genital ridges are 

 formed from the dorsal portion of the splanchnic layer, in the 

 fifth to the tenth abdominal segments inclusive. This portion 

 becomes detached from the remainder of the splanchnic layer. 

 During the development of the embryo the genital ridge gradually 



