792 THE AMERICAN NA TURALIST. [Vol. XXXVIII. 



days the latter region measured 275 in length as compared 

 with 350 \x for the mouth-part region. In an embryo at the 

 close of the twelfth day the antennae have moved forward until 

 the anterior section measures but 200 /x. The mouth-part 

 region, owing to the loss of the tritocerebral segment and the 

 reduction also taking place in the 2nd maxillary segment, meas- 

 ures 280 /X, A comparison early in the fourteenth day shows 

 that the two regions are approxmiately equal m length. This, 

 as wc should suppose from the above, is due not so much to an 

 increase 111 tlic <\7x'. ot the anterior region, as to a reduction of 

 • the mouth-part region, due to the ce- 



phalad migration of the mouth parts. 

 1 he developing pronotum of the pro- 

 thorax IS pushing rapidly forward, and 

 IS hunting the pleural region of the 

 /- . ■ , maxillary segments (l^ig. 10, /;/.). 



During the sixteenth day there 

 occurs the scries of changes which 

 Wheeler {'89) has described as the 

 I _ _ ^ ^ revolution of the embryo. This is 



.lavs. .s!.„«ing posterior tentoriliTn" ^ pcriod of vcry rapid growth, and at 



'(""th'lirm'hsm reRim'^^^^^ ^^"^^ ^^""^'^^ COmplctcd 



>.'>tuM,/r.,i,.,.s pushed forward until thc circumcresccnce of the yolk by 



niaxilU V cj " r le rs ^j^^ CmbryO. 



At about the begmning of the six- 

 teenth cLi}, just as these changes have commenced, the condi- 

 tions do not diftci markedly from what I have just described. 



Hk icdiKUon ot ilie mouth-jxu-t region is rapidly progressing, 

 the kn,L;lh ot the anterior measuring 200 ^ as compared with 

 "')0 M t.n- tlie ni,.uth-i)art reoion. The pleural region of the 

 pK'thoKw has extended torward until its most cephalic point 

 I'l^'oxu \W haM- ot the 1st maxilLx, while its indistinct spirac- 

 u'.ai uu a^^lnatlon hes oxer the base of the 2nd maxilla. The 

 ^^X^-^aW lohes have extended back until they lie well over the 

 'p' niandihles. 1 ne i st maxilla: greatly exceed the 2nd, 



''"'J^^^ '^'^'^ '^11 l^^it t^ised to tonn the labium. 

 ^ ^^n^\<.ntial \ k u ,,t eml)i\()s about this age the appendages 

 <^<>nip ae } nide the sternal region; but on carefully dissecting 



