No. 3-] THE EMBRYOLOGY OF A TERMITE. 55 I 



KorscJielt and Heider, it is found that the Tennite and certain 

 Orthoptera with superficial embryos, as is explained in this 

 paper, represent the invagifiate type of development there sug- 

 gested better than do the Libellulids, with embryos " immersed " 

 in the yolk and other secondary characters. Other methods 

 of origin of the amniotic fold are most probably derived from 

 that best exhibited by the Termite and certain Orthoptera. 



^.5. It became important for some reason (whether for 

 protection, better nutrition, accumulation of waste products, 

 etc.) associated with a new habitat or mode of life, that the 

 superficial embryos of the ancestors of the winged insects should 

 be completely covered over. The forms we may now consider 

 primitive for a number of reasons exhibit a relatively small, 

 superficial disc as the first rudiment of the embryo. Here 

 was an especially favorable condition for the earliest possible 

 appearance of the membranes, at a time when they might be 

 particularly needed. Only a few forms have retained this 

 process in a near approach to its primitive form. (I believe 

 that the amnion is formed from the rudimentary ectoderm by 

 essentially the same method, on the similar germ-discs of the 

 Termite and certain Orthoptera, though in the Termite the 

 fold is more evident at the posterior end.) Changed conditions 

 have led to a disappearance of the membranes in a few insects. 



e. 6. The ventral flexure of the first rudiment of the embryos 

 of the invaginate type which forms the amniotic fold has not 

 been proved to be of a phylogenetic significance. 



e. 7. Even if it can be shown conclusively, in the case of 

 the apterygote ^gg, that the open cavity is a somewhat nearer 

 approach to the amniotic cavity of the winged insect than that 

 found in the myriopod Qgg (or, in other words, what Heymons 

 speaks of as amnion is a derivative of the rudimentary ecto- 

 derm, as in the Termite, and not simply a part of the blasto- 

 derm comparable to that lying outside the limits of the embryo 

 in the myriopod &g^, it must be remembered that the open 

 invaginations of the myriopod and apterygota may not even be 

 due to causes similar to those calling for the closed amniotic 

 cavity of winged insects. These may be entirely distinct phe- 

 nomena with very different significance. 



