THE EMBRYOLOGY OF THE HONEY BEE 77 



part by ectoderm derived from the stomodaeal and proctodaeal 

 invaginations, a condition which could readily be interpreted as 

 constituting a transitional stage between Lepisma and the higher 

 pterygote insects. Recently Nusbaum and Fulinski (1906, 1909) 

 have reinvestigated the origin of the mesenteron in two of the 

 forms studied by Heymons, Phyllodromia (Blatta) and Gryllo- 

 talpa, and have obtained a different result, namely that the me- 

 senteron is formed from the two ends and also from the median 

 portion of the lower layer. Similar results were obtained by 

 Hirschler (1906, 1909) in the Lepidoptera and Coleoptera. Hey- 

 mons' conclusions and interpretations have also been contested 

 by Escherisch (1900) in his paper on Calliphora (Musca). Car- 

 riere and Burger's (1897) observations on the development of 

 the mesenteron rudiments in the mason bee have already been 

 mentioned (p. 71) ; Noack (1901) arrived at similar conclusions 

 in the case of Calliphora (Musca). In contrast to the results of 

 Heymons and all the other investigators of this subject Ham- 

 merschmidt (1910) finds that in the orthopteron Dixippus the 

 mesenteron is formed exclusively from the median section of 

 the lower layer, which in most insects produces the blood cells. 

 The conditions existing in the honey bee, as they have been 

 described in this paper, obviously lend little support to the views 

 of those who regard the mesenteron of insects as arising from 

 the ectoderm of the stomodaeum and proctodaeum (III), since 

 its rudiments are already formed long before the stomodaeal and 

 proctodaeal invaginations appear ; much less do they harmonize 

 with the theory of the origin of the mesenteron from yolk cells 

 (I). The relation of the mesenteron rudiments in the honey 

 bee may be interpreted in either of two ways, and the one chosen 

 will probably depend largely on the theoretical bias of the in- 

 terpreter. First, the mesenteron rudiments may be referred to 

 the mesoderm (II). Several facts can be cited in support of 

 this view, for example : the continuity of the middle plate and 

 the mesenteron rudiments during the earlier stages in their for- 

 mation, and the fundamental similarity in the manner of for- 

 mation of both the mesenteron rudiments and the mesoderm, all 

 being formed by a contemporaneous inward migration of ele- 

 ments of the blastoderm. Second, the mesenteron rudiments 

 may be considered, with Carriere (IV) as purely blastodermal 



