THE EMBRYOLOGY OF THE HONEY BEE 201 



next stage (XI). The rudiment of the enteric muscles (Fig. 80. 

 MclEnt) increases in extent and decreases in thickness. The 

 rudiments of the first and second sections of the fat body become 

 more clearly defined, the first section almost losing its connection 

 with the splanchnopleure (MclEnt), while the second breaks up 

 into its constituent cells. The rudiment of the dorsal diaphragm 

 now finally parts company with the remainder of the somatic 

 layer of the mesodermal tubes, and together with the rudiment 

 of the enteric muscles, forms in section a figure comparable to an 

 inverted V. The apex of the V is formed by a group of small 

 cells, the cardioblasts (CM), whose fate is that of forming the 

 two halves of the heart. In the section figured the rudiments 

 of three sets of muscles are plainly evident by reason of their pale 

 appearance and small nuclei. The dorsalmost and iargest of 

 these is that of the dorsal longitudinal muscles (DLMcl), below 

 this, lying between the tracheal trunk (TraTr) and the hypo- 

 dermis, is the rudiment of the oblique muscles (OMcl), while next 

 to this, ventrad of the silk gland (SlkGl) is the rudiment of the 

 ventral longitudinal muscles (VLMcl). Between this last and the 

 hypodermis, laterad of the ganglion of this segment is a small 

 group of pale cells, which constitute the mesodermal portion of the 

 leg rudiments (Mcso^L). The yolk continues to contract and its 

 ventral half assumes a three-sided form, and the future body 

 cavity becomes greatly increased in extent. The rudiments of all 

 the mesodermal tissues and organs are now well differentiated 

 from one another and during this stage and the one following 

 (XII), they increase in size and together with the hypodermis 

 extend rapidly dorsad, this movement leading finally to the com- 

 plete enclosure of the yolk by the germ band at Stage XIV. The 

 most noticeable change at Stage XI is seen in the rudiment of 

 the enteric muscles (MclEnt). At the preceding stage this rudi- 

 ment covered only an insignificant part of the yolk. The rudi- 

 ment of the mesenteron (Mint) has, since Stage IX (Fig. 78) 

 covered the dorsal side of the yolk, but not until Stage XI does it 

 come into contact with the rudiment of the enteric muscles. At 

 this stage however it begins to extend rapidly ventrad over the 

 yolk — which now is cylindrical in form — insinuating itself between 

 the latter and the muscle rudiment. At Stage XII (Fig. 81, 



