548 



KNOWER. 



[Vol. XVI. 



of the entire extra-embryonal region as a serosa, before the 

 doubling-up takes place. As this happens, he says (in a para- 

 graph on page 587 of his paper) that the cells of the edges of 

 the embryonic band become pulled out into a thin cellular 

 membrane, the amnion. None of his figures, however, give 

 proof of such a process of transformation of a part of the 



ex. 



..ex. 



■mp. 



Fig. 3. Fig. 4. 



Diagrammatic figures (sagittal sections), comparing the " primary ventral flexure " (" doubling- 

 up," or invagination) of the myriopod and apterygote embryos with the amniotic fold 

 of the winged insect, (i) Myriopod (Julus) embryo, at the first appearance of the 

 ventral flexure ; (2) similar stage of the embryo of Lepisma (apterygote) ; (3) early 

 amniotic fold (doubling-up, or invagination) of the unspecialized embryonic rudiment 

 of the Termite ; (4) later stage of the Termite embryo, after the closure of the amniotic 

 cavity — a stage similar to that of the two types in i and 2, but the " tail-piece " is straight 

 here. ex. extra-embryonal blastoderm ; e.p. posterior, unspecialized ectoderm ; m.p. 

 posterior, unspecialized mesoderm ; a.s. segmented region anterior to unspecialized tissues 

 of " tail-piece " ; cA. chorion ; y. yolk ; in 3, /.e. primitive, unspecialized ectoderm of germ- 

 disc ; am. amniotic fold in undifferentiated ectoderm ; in 4, se. serosa ; am. amnion. 



embryonic, rudimentary ectoderm into the amnion, as observed 

 in the winged insects. The figures show no more as to this 

 question than that, as the embryonic band sank into the yolk, 

 the extra-embryonal cellular membrane attached to its edges 

 was pulled along. 



The result, as figured, is a band doubled-up like that of the 

 myriopods, and not differing from this except in lying deeper in 



