50 THE EMBRYOLOGY OF THE HONEY BEE 



ski 1871) Musca (Kowalevsky 1886), Pyrrhocoris (Graber 

 1888a), Chalicodoma"' (Carriere 1890). 



2. The middle plate remains nearly flat and is overgrown by 

 the edges of the lateral plates, which become free. This type is 

 relatively uncommon but is also found in representatives of 

 widely separated orders, as in Apis, Sphinx (Kowalevski 1871), 

 Pier is (Bobretsky 1878), Gasteroidea (Gasterophysa) (Lecail- 

 lon, 1897), 9 and, in a slightly modified form in Forficula (Hey- 

 mons 1895). 



3. The mesoderm arises by proliferation and immigration from 

 a median area of the ventral blastoderm. A median groove is 

 often also present. This type approaches the conditions obtain- 

 ing in the Apterygota (Heymons 1897, Uzel 1898) and appears 

 to be especially characteristic of the Orthoptera, being found, 

 for example in Gryllotalpa (Korotneff 1885), Phyllodromia 

 (Cholodkowsky 1891b), Gryllus, Periplaneta (Heymons 1895). 



It is accordingly evident that Apis, in the manner in which it 

 forms the mesoderm, while agreeing with representatives of 

 remotely allied groups, differs from its near relative Chalicodoma. 

 Very little systematic importance can therefore be accorded to 

 these differences. Carriere and Burger, however, took the op- 

 posite view and on the basis of their observations in Chalicodoma, 

 declared their belief that the observations of Kowalevski and 

 Grassi in regard to the formation of the mesoderm were in- 

 correct on account of imperfect technique, and that a reinvesti- 

 gation of Apis with modern methods would show that the meso- 

 derm was formed in the same manner as in Chalicodoma. It is 

 now sufficiently evident that this assumption was unfounded, at 

 least so far as the eggs destined to form workers or queens are 



8 Carriere (1890, 1897) regards as the middle plate only the inner layer 

 of the two layers of cells which form the mesoderm, the outer layer being 

 considered as formed toy the infolding of the mesial portions of the lateral 

 plates. Comparison with the corresponding stages of other insects in 

 which the mesoderm is found by a median invagination, as Hydrophilus 

 for example, indicates that this distinction is hardly justified, and that 

 in all cases the term middle plate may properly be considered as including 

 all of the infolded median portion of the ventral plate, and therefore all 

 of the material for the mesoderm. 



'According to Hirschler (1009a) the mesodeim in Gasteroidea is 

 formed by infolding, as in Hydrophilus. 



