ORIGIN OF THE SALIVARY GLANDS 



571 



suggest that they were originally dermal glands, whose mouths 

 became drawn into the buccal .. 



If, ! r 



cavity. 



For their serial arrangement, see 

 p. 337. Korschelt and Heider state that 

 they would be inclined to homologize 

 the salivary glands of insects with those 

 glands of myriopods opening into the 

 mouth-cavity, were it not that these 

 glands in myriopods opening into the 

 mouth are in reality transformed neph- 

 ridia originating from the mesoderm, 

 while the salivary glands of insects are 



JK- 



FIG. 545. Cross-section through the abdomi- 

 nal region of an embryo of cockroach (P. ger- 

 manica) after the yolk has been completely 

 enclosed by the primitive band and the closure 

 of the back ; /*, tracheal stigma ; other letters as 

 in Figs. 540, 544. This and Fig. 544 after Hey- 

 mons, from Korschelt and Heider. 



FIG. 546. Embryo of Doryphora shortly 

 after the appearance of the appendages, unrolled 

 and isolated : o, stomodaeum ; Ib, labrum ; b 1 -^ 3 , 

 three brain segments ; og^-og 3 , three segments of 

 the optic ganglion ; op^-ojP, three segments of 

 the optic plate ; fl-t s , five pairs of invaginations 

 which form the tentorium, etc.; 7 -< 20 , tracheal 

 invaginations; the two last pairs (* 19 , t m ) either 

 disappear or form the openings of the sexual 

 ducts ; at, antenna; ; tnd, mandibles ; mx^-nur^, 

 maxillae ; p l ^j> 3 , legs ; c, commissure connecting 

 the two ganglionic thickenings (g l ) of the pre- 

 mandihular segment ; gl, ganglia ; mat, middle- 

 cord thickenings ; mpg l -mpg 3 , rudiments of 

 three pairs of urinary tubes ; a, proctodseum. 

 After Wheeler. 



