THE EMBRYOLOGY OF THE HONEY BEE 219 



subsequently confirmed by several investigators ('Friederichs 

 1906, Hirschler 1909, Hegner 1908). 22 



In the light of all of these observations, which relate to members 

 of five of the orders of the insects, it seems probable that in all 

 insects the germ cells are segregated at an early period. This is 

 also in harmony with modern investigations on certain other ani- 

 mal forms, as for example those of Boveri (1887) on the round 

 worm Ascaris, and Hacker (1897) on the crustacean Cyclops. 

 In all of those insects, however in which an early segregation of 

 the germ cells has been directly observed, these cells are more or 

 less readily distinguishable by means of differences in size, clear- 

 ness, etc. This is quite evident from the figures given by Wheeler 

 (1893) and Heymons (1895), and is especially well shown by 

 an original figure by Henneguy (1904, Fig. 378). In many 

 insects the sex cells closely resemble the other cells of the embryo. 

 This was found by Heymons to be the case in Periplaneta orien- 

 talis and in Gryllus. In these instances however the early segre- 

 gation of the germ cells can be safely inferred by a comparison 

 with closely related forms in which this difficulty was not en- 

 countered. In the honey bee there is, as a rule, little difference 

 between the cells of different tissues and organs at the earlier 

 stages. As has already been stated, the cells which are to consti- 

 tute the ovary are at first indistinguishable from those of the meso- 

 derm. It does not however follow that they are of mesodermal 

 origin, even although they seem to constitute a portion of the 

 mesoderm, since it is not at all unlikely that the germ cells may 

 be set aside at an early period in development, and afterwards 

 migrate into the visceral wall of the mesodermal tubes, and that 

 such a migration may take place unobserved, on account of the 

 similarity of the sex cells and mesoderm cells. A solution of this 

 problem is perhaps to be found in the discovery of some constant 

 difference hitherto unobserved, between the sex and other cells. 

 An approximate solution is probably easier. If a closely allied form 

 should be found in which the germ cells can be recognized with- 

 out difficulty, then the behavior of the germ cells in the honey bee 

 could be inferred by analogy. 



22 A complete review of the literature on this subject may be found in a 

 recent paper by Hegner (1914). 



