THE EMBRYOLOGY OF THE HONEY BEE 199 



changes in form. The cells of the mesodermal tubes have lost 

 their columnar shape and from the inner layer a ridge now pro- 

 jects abutting against the yolk, directed mesiad and ventrad, the 

 splanchnic layer or rudiment of the enteric muscles (MclEnt). 

 Near the mid-line the yolk has receded a trifle and the mesoderm 

 as such has disappeared, leaving a narrow space between the 

 ectoderm and yolk, the epineural sinus (Heymons 1895) which is 

 partially filled with large loose cells, the blood corpuscles (BIC). 

 At Stage X (Fig. 79) the rudiments of all the mesodermal 



G'ng 



Fig. 79. Transverse section through the third trunk segment of an 

 embryo, Stage X, x 387. 



organs and tissues may readily be identified. The splanchnopleure 

 or rudiment of the enteric muscles (MclEnt) has changed from a 

 mere ridge to a well defined layer pressed close against the yolk. 

 The cells of the remainder of the visceral layer have for the most 

 part lost thir epithelial character and show a looser arrangement, 

 in anticipation of their destiny, which is to form the two main 

 divisions of the fat body (iF, 2F). Moreover a break in the 

 visceral layer is seen opposite the rudiment of the tracheal trunk 

 (TraTr). At the mesial edge of the mesoderm, close to the 

 ganglion of this segment (Gng), two groups of extremely small 

 cells are seen ; these are the rudiments of the ventral longitudinal 



