108 MISC. PUBLICATION 631, U. S. DEPT. OF AGRICULTURE 



stage I (Stages I to III of Laake) 



1; Mouth hooks with the anterior end directed forward and blunt, and 

 with the posterior end divided by a shallow incision into 2 blunt 

 lobes (fig. 54, A) diana Brauer 



Figure 54. — Mouth hooks and anterior part of cephalopharyngeal skeleton of 

 first-stage larva: A, Hypoderma diana; B, H. lineatum ; C. H. bovis. (A re- 

 drawn from Schuiid (132, p. 231) ; B and C after Bishopp and coworkers (18). 



Month hooks with the anterior end directed outward and the posterior 



end not divided into 2 lobes . 2 



2. Mouth hooks with the anterior end sharp and undivided; a pointed, 

 recurved tooth some distance behind the anterior end (fig. 54, B) 



lineatum (Villers) 

 Mouth hooks with the anterior end divided into 2 blunt lobes ; no recurved 

 pointed tooth (tig. 54, C) bovis (Linnaeus) 



stage II (Stage IV of Laake) 



Stigmal plates of posterior spiracles orange or yellowish brown ; the 

 discs separate or loosely connected, 12 to over 20, but usually 18 to 25, 

 in number lineatum (Villers) 



Stigmal plates of posterior spiracles brown to black; the discs closely 

 grouped together and fused, 29 to over 40, usually 32 to 37, in number. 



bovis (Linnaeus) 



stage III (Stage V of Laake) 



1. Tenth segment devoid of spines above and below; the posterior 

 stigmatal plate deeply excavated funnel-like toward the button (fig. 

 55, A) bovis (Linnaeus) 



Figure 55. — Posterior spiracles of mature larva : A, Hypoderma bovis; B, H. 

 lineatum. 



Tenth segment with spines ventrally ; the posterior stigmatal plate more 



shallowly excavated toward the button (fig. 55, B) 2 



2. Segment 10 ventrally with an anterior row but without a posterior band 

 of spines ; segments 8 and 9 dorsally without posterior bands of spines ; 

 the posterior spiracles divergent (figs. 56, A 57, A )_„.,_, diana Brauer 



