THE EMBRYOLOGY OF THE HONEY BEE 69 



It cannot fail to be noticed that there is a fundamental simi- 

 larity between the formation of the mesenteron rudiments and 

 of the mesoderm, since all three arise by an inward movement of 

 cells of the ventral plate. Moreover, the latter is continuous 

 cephalad and caudad with the mesenteron rudiments during the 

 period of their formation. 



The origin of the mesenteron in the honey bee was first dis- 

 cussed by Biitschli (1870). Biitschli believed it to be produced 

 like the blastoderm by the so-called "free cell formation." 11 Re- 

 ferring to a stage nearly corresponding to that numbered VIII 

 in this paper he says (pp. 540-541) "the formation of the mid- 

 intestine has already commenced, yet, as I often observed in 

 much more advanced embryos, only on the dorsal side of the 

 yolk ; seen in optical section, it is a single layer of close pressed, 

 yellowish cells. It appears to me that this cell layer takes its 

 origin near the ends of the germ band, since its thickness is 

 here greater than in the middle region. I have not succeeded in 

 observing its beginning, but in regard to it must conclude with 

 Zaddach and Weismann that the mid-intestinal wall develops 

 by free cell formation and not by delamination of an inner cell 

 layer." It is interesting however to find that Biitschli both noted 

 and figured the anterior mesenteron rudiment, although without 

 recognizing it as such. He says concerning it (p. 529) : "In 

 connection with the regression of the germ band at the anterior 

 pole is a thickening found there, concerning the true significance 

 of which I am not sure ; seen en face it appears rounded, in 

 profile, it projects inward, yet I believe that the hemispherical 

 swelling represented in figure 10B is not in reality such, but that 

 the lateral extension of the thickening has produced an optical 

 illusion." The figure referred to corresponds to a stage about 

 midway between Stages V and VI. 



Kowalevski (1871) believed that the mesenteron in the bee 

 owed its origin to the inner or splanchnic layer of the mesoderm. 

 He was evidently led to this belief by the fact that in sections the 



11 This consists in the spontaneous formation of nuclei within a proto- 

 plasmic matrix. It is hardly necessary to say that such a process does not 

 exist, every cell arising by division from a preexisting cell. The belief 

 was due to the imperfect technique employed by the investigators. 



