122 THE INTEGUMENTAL SKELETON OF THE IMAGO. 



The Antennae hang vertically in front of the mesofacial plates; 

 they are usually said to consist of three joints and a bristle. 

 They are really six-jointed, as Desvoidy pointed out, with a 

 greatly enlarged third joint, the three terminal joints being 

 reduced to the form of a three-jointed bristle. The large third 

 joint is cylindroid, and slightly prismatic. It contains a 

 complex sensory organ, which is undoubtedly olfactory (see 

 ' Sensory Organs '). 



The Posterior Surface of the head capsule consists of the 



FIG. 24. /, The Face of the Blow-fly : ep, epistome ; /j facial edge of paracephalon ; 

 ///, lunula ; tnf, mesofacial plate ; r, rostrum ; /;-, torulus. 2, the Metacephalon 

 of the same : /', basal sclerite or gula ; bs, basal suture ; cf, cotyloid cavity ; dr, 

 dorsal ring ; ep a, epioccipital sclerites ; y 1 ancly' 2 , first and second jugulares ; ju, 

 jugum ; p s, paracephalic suture. 



posterior part of the paracephala (Figs. 23, ./, /, and 24), the 

 occipitals of Menzbier, the epicephalon (m), the pars basilaris 

 (b], and the metacephalic ring surrounding the occipital fora- 



men. 



The occipital, or metacephalic, ring (Fig. 24) consists of two 

 lateral parts, and of a dorsal and a ventral arch. 



The lateral parts are concave externally and convex inter- 

 nally ; they each give off a process to form the jugum, and are 



