No. 3-] THE EMBRYOLOGY OF A TERMITE. 553 



accepting a fundamental common cause connecting the two 

 invaginations, abandoned further comparison. 



Heymons (15) has quite recently claimed to have carried this 

 a step further, in a manner which I have already considered. 



If we proceed from the assumption that some like necessity 

 of removing the embryo from surface insults, or of furnishing 

 it with better conditions of nutrition, etc., caused an invagina- 

 tion of the embryo of the myriopod (or apterygote) and of the 

 superficial rudiment of the ancestral winged insect, it is pos- 

 sible in the case of the Termite embryos at an early stage, just 

 before the closure of the amniotic cavity, to make a comparison 

 of a somewhat different nature from what has hitherto been 

 suggested. 



The condition found in the Termite permits us to see how 

 we may retain an essential feature of Will's idea (also Wheeler's) 

 of a derivation of the amnion from a portion of the ancestral 

 myriopod's embryonic tissue, in association with a process of 

 invagination, without involving the further idea of a transforma- 

 tion of definitively organized tissue, with the disappearance 

 of segments and the migration of the anus. It will, however, 

 be found that the following is not an effort to trace the amnion 

 in a phylogenetic sense back to the myriopod. 



Referring back to the text-figures, we find practically the 

 same condition in the three first diagrams — a doubled-up, com- 

 paratively thick embryonic band, enclosing a cavity which opens 

 on the surface of the ^gg. In the Termite this opening in 

 Text-fig. 3 closes, and the outer wall of the cavity, which is 

 a portion of the ectoderm of the first rudiment of the embryo, 

 becomes the amnion. (See fourth text-figure.) 



It is evident that if the invagination of the winged-insect 

 embryo is to be derived from that in the myriopod (or aptery- 

 gote) ^gg, the amnion of the insect most probably arose from 

 some portion of the thickened, unspecialized (striped in the 

 text-figures) ectoderm of the myriopod (or apterygote) ancestor. 



My idea is that, since it has been shown that the amniotic 

 fold of the Termite is a specialized portion of particularly the 

 posterior ectoderm of the embryonic rudiment, at a very early 

 stage, before elongation begins and before the appearance of 



