No. 3-] THE EMBRYOLOGY OF A TERMITE. S57 



myriopod embjyo, at an especially early period, fi'om the primitive 

 unspecialized ectoderm of an ancestral disc-shaped rudiment. It 

 arises especially in a posterior region of the early ectoderm of the 

 Termite. A similar primitive origin may, however, be associated 

 with the sinking of the embryonic rudiments of other insects 

 {especially in the forms I have taken as primitive), where the 

 folding occurs in other portions of the early ectoderm, for it must 

 be remembered that snch ectoderm can produce lateral as well as 

 serial organs. 



The less number of segments in the winged-insect or aptery- 

 gote, as compared with the myriopod, was attained, as far as 

 the embryology shows, by an arrest in a primitive method of 

 growth common to arthropods and similar to budding, which 

 was continued for a longer time in the many segmented 

 ancestors of insects. 



The reason for the shorter duration of this process in the 

 later group is not known, but must be sought in such related 

 fundamental problems of growth as regeneration of lost parts, 

 metamerism, and the cleavage of the ovum. 



e. 9. As has been said, the ventral flexure of myriopod 

 embryos of the present time may be proved later to be con- 

 nected in no sense with an amniotic fold. Even if such turns 

 out to be the case, the above comparison will then have served 

 a good purpose, in calling attention to a plausible interpretation 

 of the amniotic fold as originating primarily by invagination in 

 winged-insects, independently, and not traceable to any previous 

 similar phenomenon. 



e. 10. If the above view is applied to the vertebrate amnion, 

 the participation of both primary and, at the point of origin of 

 the fold, undifferentiated layers of the body-wall would be under- 

 stood in a sense similar to the formation of other early organs, 

 in which both primary layers cooperate. 



Explanatory Note. 



This paper was accepted as a thesis. May, 1896. It was 

 abstracted in XhQ Johns Hopkins University Circulars, Vol. XV, 

 June, 1896. Unavoidable delay in publishing and a renewed 



