92 THE EMBRYOLOGY OF THE HONEY BEE 



the cephalo-dorsal body being here represented by the "Rz" cells. 15 

 At Stage X the vestiges of the cephalo-dorsal body may still be 

 seen lying beneath the dorsal wall of the mesenteron, but they 

 soon become indistinguishable from the elements of the yolk, and 

 unquestionably like them suffer ultimate absorption. The cephalo- 

 dorsal body was first seen by Grassi (1884), who has represented 

 it in figure I of Plate X, but did not mention it in the text. Dickel 

 (1903) was the first to describe this body, which he named the 

 "yolk plug," since he regarded it as derived from yolk cells which 

 migrated to its point of origin, this point being designated as the 

 blastopore. The "yolk plug" was regarded by Dickel as the an- 

 terior mesenteron rudiment. This assumption was founded on the 

 circumstance that the "yolk plug" had disappeared at the time 

 when the anterior mesenteron rudiment came into prominence. 

 It will hardly be necessary to say that this assumption is wholly 

 wrong, and must have been due to defective observation, since 

 any series of sections showing the "yolk plug" should also show 

 the true anterior mesenteron rudiment, since in fact the "yolk 

 plug" becomes evident only after the anterior mesenteron rudi- 

 ment has begun to be formed. Moreover, the remnants of the 

 cephalo-dorsal body ("yolk plug") are plainly evident long after 

 the anterior mesenteron rudiment is fully formed. 



Petrunkewitsch (1902), in a paper on the fate of the polar 

 bodies in the drone egg, describes and figures a body formed in 

 the cephalo-dorsal region of the egg by cells termed for brevity 

 f( Rs-ce\\s" which owe their origin to a single cell formed by the 

 union of the second polar body with the inner half of the first. 

 This structure formed by the "Rs-ce\ls" apparently agrees closely 

 in form, structure and position with the cephalo-dorsal body of the 

 worker egg. Petrunkewitsch, however, states that he did not 

 find this body in worker eggs, and gives a figure to illustrate this 

 statement, but this figure (4) is obviously of an earlier stage than 

 those in which is found either the cephalo-dorsal body or that 

 formed by the (c Rz-ce\\s" The fate of the latter according to 

 Petrunkewitsch's account, is as follows : It first sinks below the 



15 Petrunkewitsch (loc. cit.) states that mitotic figures were found in 

 this cell mass. The writer has never seen them in the cephalo-dorsal body 

 at any stage. 



