550 KNOWER. [Vol. XVI. 



shown to exhibit this phenomenon similar to the myriopods — 

 an important point in itself, indeed, if the amniotic fold of the 

 winged insect is to be derived from an earlier invagination. 



Willey differs with Heymons as to interpreting the ventral 

 flexure of the embryo of Lepisma as comparable with the later 

 caudal flexure of insect embryos. Without admitting his 

 theory of the trophoblast, I must agree with Willey in this 

 distinction. 



In many respects the development of Lepisma bears a close 

 resemblance to that of the primitive Orthoptera and the Ter- 

 mite. It is interesting to find the germ-disc originating at the 

 posterior pole of the ^^g as in the Termite. The absence of a 

 gastrula groove, in connection with the origin of the meso- 

 derm, is also in agreement with what Fleymons has found in 

 some Orthoptera, and with the results here submitted for the 

 Termite. 



E. The conclusions reached from the above general review 

 of the question before us, in the light of my own special obser- 

 vations, and again referring to my views, expressed in a pre- 

 vious section of this paper, as to the primitive type of insect 

 development, may be summed up as follows : 



e. I . The amniotic fold did not arise as a necessary result of 

 any combination of purely mechanical forces which has been 

 formulated up to the present time. 



e. 2. The amnion and amniotic cavity of insects are adaptive 

 structures, which, as far as our knowledge now goes, arose first 

 in the winged insects as a response to some definite need of 

 the developing embryo. 



e. 3. The amnion is primitively a derivative of the rudimen- 

 tary embryonic ectoderm. 



e. 4. An <' invaginate" type of development is the more 

 primitive one for insects. Irrespective of its relation to the phe- 

 nomenon of doubling-up of the myriopod or apterygote embryo, 

 it has been shown to be associated with the more primitive 

 insects, and the most primitive (probably) method of mem- 

 brane formation outlined in paragraph 5 below. 



It must be added to this, that m the light of researches of a 

 7nore recent date than that of the publication of the text-book of 



