196 
EXPLANATION OF PLATE XVIII 
1 ig. 2(>. Section through closed labella at the junction of the fork (i) 
with the ventral sclerities (/). x 750. 
1 ig. 27. Section through the labium in the plane where the ventral 
sclerites ( f ) first appear. The fine hairs at the apex of 
these organs are here shown, x 750. 
I ig. 28. Section through the labium at the plane where the labruni 
(<7) first appears. Here muscular bands stretch across from 
the ventral sclerites to the walls of the labial gutter, x 150. 
