3i3] TARVAE OF THE TENTHREDINOIDEA—YUASA 15 



and the Tenthredininae; with long setae as in Pteronidea; or with abund- 

 ant conspicuous setae as in Monophadnoides and the Cladiinae. The 

 setae tend to be more numerous and longer on the ventral portion of the 

 head. The number and location of the setae on the head vary with the 

 individuals, excepting those on the clypeus and labrum, but their general 

 characteristics, such as relative abundance, manner of distribution, 

 and the kind of setae, are constant within genera and subfamilies. The 

 head may be pale, creamy white, or light brown, but oiften in life appears 

 as green or greenish white on account of the greenish blood showing thru 

 the cuticle, or it may be blackish or brownish with or without distinct color- 

 markings. The darker color is due to a deposition of colored pigments in 

 the cuticle and is generally permanent in alcoholic specimens. The color 

 and the coloration of the head are generally constant specific characters. 

 There are, however, ontogenetic changes in these respects. The very young 

 stages may be lighter in color and later stages darker, or vice versa as in 

 Cimbex, or all stages except the last instar may be darker and the ultimate 

 stage greenish as in Pteronidea ribesii. The color markings may be diffuse 

 in the young and become localized and definite in older stages, as in some 

 species of Dolerus, or they may vary from faint spots to general contiguous 

 markings as in certain species of Strongylogaster. The more common mark- 

 ings are brownish spots on the dorsum of the vertex, on the front, and often 

 caudad of each ocellera. There may be a stripe along the epicranial stem 

 and vertical furrows or dorsad of the ocellarae. When the head is darkly 

 colored the clypeus is usually lighter in color than the other parts of the 

 head. 



The head is usually exposed, but there is a tendency in the leaf-miners,, 

 wood-borers, and a few others to have the cephalic end of the prothorax 

 produced into a broad fold on the dorsal and lateral aspects. This fold 

 covers the caudal portion of the head as in Tremex, Metallus (Fig. 35), 

 and Caliroa (Fig. 69). 



The structures of the head will be discussed under two sections, one 

 dealing with the fixed parts, that is all the immovable parts of the head- 

 capsule, and the other dealing with the movable parts — the antennae and 

 mouth-parts. The fixed parts include the vertex, front, clypeus, labrum, 

 occiput, and postgenae, together with their bounding sutures, ocellarae, 

 and tentoria. 



Epicranial Suture. — The inverted Y-shaped median suture of the head 

 is the epicranial suture. The stem (es) of the Y originates at the occipital 

 foramen, extends cephalad, dividing the vertex into halves, and bifurcates 

 on the cephalic aspect of the head. Each arm of the bifurcation (ea) 

 extends obliquely laterad for a short distance and then bends ventrad 

 to the ventral margin of the head, terminating near a precoila. The 

 epicranial suture is present in all larvae except those of the Xiphydriidae 



