56 THE EMBRYOLOGY OF THE HONEY BEE 



orders, and termed by him "macrosomites," on the occurrence of 

 which Graber has attempted to construct an elaborate theory of 

 segmentation applicable to the entire arthropod phylum. 



10 



2. Formation of the rudiments of the mid-intestine.^ 

 The mesenteron or mid-intestine in the honey bee is derived 

 from two rudiments, arising at the anterior and posterior ends 

 of the germ band respectively. The anterior mesenteron rudi- 

 ment, owing to its position, is much more readily observed and 

 studied than the posterior mesenteron rudiment, and therefore 

 will be described first. 



It will be remembered that the lateral folds end abruptly 

 toward the cephalic pole, leaving vacant an area of the ventral 

 plate about as long as the egg's diameter at this point, corre- 

 sponding to the anterior field of Chalicodoma (Carriere and 

 Burger 1897). At a stage a trifle older than Stage IV, on 

 surface view there may be observed a darker area along the 

 mid-line in this field. This darker area, narrow and rather 

 vaguely outlined at first, rapidly increases in size, density and 

 definiteness until at Stage VI it presents the appearance shown 

 in the figure (VI, AMR). Cf. also Figs. 24A and B). Its out- 

 line is that of a short ellipse, with its longer axis directed length- 

 wise of the egg; in stained preparations it is deeply stained and 

 very conspicuous. Its width approximates that of the anterior 

 end of the middle plate, with which, at this time, it has come 

 into contact. This is the anterior mesenteron rudiment. Fig- 

 ures 25A to D represent transverse sections through the middle 

 of this rudiment at four successive stages of its development. 

 The first of the series, A, is taken from Stage IV, just before 

 the anterior mesenteron rudiment becomes visible from the ex- 

 terior, and at its earliest recognizable stage. In the mid-line, 

 over an area whose breadth is about one-eighth of the circumfer- 

 ence of the egg at this point the blastoderm cells, hitherto long 



10 These have been very widely identified by embryologists as entoderm, 

 and accordingly termed such. Since however there is some doubt as to 

 the correctness of the homology of these rudiments with the entoderm 

 in other classes of animals it has seemed preferable to avoid the use of the 

 term "entoderm" in connection with the development of pterygote insects 

 and, for the present at least, to simply use the term "mesenteron rudi- 

 ments." See discussion at end of this section. 



