No. 3-] THE EMBRYOLOGY OF A TERMITE. 555 



Turning finally to the two lower text-figures of the develop- 

 ing Termite embryo, we recall that the germ-disc, when the 

 amnion first folds up and before the closure of the amniotic 

 cavity, is in a very undifferentiated state. (The suggestion is 

 made in a previous section of this paper (i?, p. 30) as to the 

 comparatively primitive nature of this small rudiment.) I have 

 indicated in the diagram illustrating this stage (Text-fig. 3) that 

 the entire rudiment, ectoderm and mesoderm, is quite unspe- 

 cialized. The upper layer is striped, as is the ectodermic tissue 

 of a similar early stage in differentiation in the "tail-piece" of 

 the other figures. The lower layer is also an unspecialized 

 mass. 



The condition of the tissues is just what was found in a 

 much later stage of the myriopod (or apterygote), in the partic- 

 ular region where the ventral flexure occurs (Text-figs, i and 2). 



A first difference is, that though the flexure takes place at 

 a corresponding stage in the differentiation of the tissues, it 

 occurs at a much earlier period in the development of the 

 winged insect ; in fact, at what I have pointed out is the earli- 

 est possible stage for the origin of an amnion. Another and 

 second point is that only the ectoderm is here concerned in the 

 flexure. Thirdly, if a posterior portion of the primary unspe- 

 cialized ectoderm becomes amnion, what will be the effect on 

 the further development of the embryo } 



The first point of difference, the relatively very early appear- 

 ance of the flexure in case of the insect, may be unimportant ; 

 since the two invaginations before us develop at a like stage 

 in the differentiation of corresponding tissue (see text-figures). 

 We have suggested apparently good reasons for an especially 

 early folding, or invagination, of the superficial rudiment of the 

 ancestral winged insect. Text-fig, 3 shows this taking place 

 before any segments have been differentiated. 



As to the second point, in regard to the ectoderm, it must 

 be first recalled that Heathcote's Fig. 30 for Julus indicates a 

 special participation of the ectoderm in the flexure, when first 

 beginning. Further, in both the myriopod and the apterygote 

 on the one hand, and the winged insect on the other, there is 

 a marked separate though associated development in the upper 



