THE EMBRYOLOGY OF THE HONEY BEE 227 



cal posterior side, lengthens out to constitute the papillate or 

 tongue-like process previously mentioned (p. 220). This is plainly 

 shown, although not lettered, in figure XIII, and lies behind the 

 labrum, bounded laterad by the mandibles and first maxillae. 



The development of the different portions of the digestive 

 canal from their respective rudiments corresponds essentially 

 to that found in other insects having bipolar mesenteron rudi- 

 ments, except in one particular. In all the other insect embryos 

 thus far studied, in which bipolar mesenteron rudiments occur, 

 including the mason bee, each of the rudiments sends out a pair 

 of epithelial bands, one on each side of the ventral mid-line. These 

 grow toward each other, meet and fuse. The narrow space left 

 vacant betwen them on the ventral side is next filled by cells de- 

 rived from the bands. The ventral surface of the yolk is therefore 

 covered first, and the dorsal surface is covered subsequently by 

 gradual dorsad growth and extension of the bands. In the honey 

 bee, as Grassi (1884) discovered, it is the dorsal surface of the 

 yolk which is first covered by the extension of the mesenteron 

 rudiments ; moreover, these extensions do not have the form of a 

 pair of bands, although certain statements made by Grassi suggest 

 this, so that Carriere (1897) has interpreted Grassi as stating that 

 each of the two mesenteron rudiments gives rise to "paired lateral 

 arms." Grassi's statement with reference to the anterior "ento- 

 derm'' rudiment is as follows: "It is always more advanced 

 on the sides than in its median part, so that two or three 

 tranverse sections are always found in which it fails to occur 

 in the mid-line/' Further on in the same chapter he makes a 

 similar statement regarding the posterior "entoderm" rudiment. 

 Examination of series of tranverse sections of Stage VIII have 

 failed to completely confirm these statements. During this period 

 of rapid growth the epithelial layers formed by the two rudiments 

 of the mesenteron are extremely irregular and variable in thick- 

 ness, especially in the region of the rapidly advancing thin edges 

 on the dorsal side of the yolk. In two of the four preparations 

 of the same stage as figure 87 the statement of Grassi seemed 

 to hold, while in the other two the advance seemed greatest along 

 the mid-line. The point is however a trivial one since Grassi's 

 statements cannot be fairly construed to indicate the presence of 

 paired bands. Evidences of these, as such, seem to have almost 



