THE EMBRYOLOGY OF THE HONEY BEE 87 



the embryo thus becomes covered by two separate layers, one 

 enclosing the entire egg, the serosa, and one covering only the 

 embryo, the amnion. The amniotic fold, the common rudiment 

 of the amnion and serosa, does not usually develop simultaneously 

 around the entire margin of the embryo, but appears commonly 

 first at its anterior and posterior ends, thus forming a cephalic 

 and a caudal fold. These conditions may be considered typical 

 of the majority of pterygote insects. There are, however, some 

 exceptions of which the honey bee is an example. Here, as is al- 

 ready apparent, but one envelope is* present, which, since it covers 

 the entire egg inclusive of the germ band, is therefore comparable 

 to the serosa rather than to the amnion. This is the opinion held 

 by Heider (1891). The term amnion nevertheless has been ap- 

 plied by both Butschli and Grassi to the single embryonic envelope 

 of the honey bee, and it therefore seemed inadvisable to change it. 



In addition to the honey bee, embryonic envelopes have been 

 observed in the following representatives of the non-parasitic 

 Hymenoptera : Formica, Myrmica (Ganin 1869), Polistes, Form- 

 ica (Graber 1888), Hylotoma (Graber 1890), CJialicodoma. 

 Polistes (Carriere 1890, and Carriere and Burger 1897), and 

 Camponotus (Tanquary 1913). Graber states that two embryon- 

 ic membrances were found in all the three forms studied by him. 

 On the contrary Carriere and Burger (1897) explicitly state that 

 in one of the forms studied by Graber, Polistes, only one embryon- 

 ic membrane is present. This is also the case in Chalicodoma. 

 In the ants but one membrane is found, according to both Ganin 

 (1869) and Tanquary (1913). 



In some of the parasitic Hymenoptera, for example Biorhisa, 

 Rhodites (Weismann 1882) Platygaster (Klulagin 1897), an 

 embryonic membrane is formed which is also single, but the forma- 

 tion of this — at least in the case of Platygaster, — is so peculiar 

 and so different from that found in other insects that its homology 

 with the embryonic membrane of non-parasitic insects is perhaps 

 open to question. 



Concerning the fate of the amnion in the honey bee the only 

 data given by previous observers are those of Butschli (1870) 

 who says (pp. 533-534) : "This envelope persists during the 

 entire development of the embryo, and like the egg envelopes 



