■ PLAXT-HOUSK ALEYROBES. ' 93 



tfom this point it passes posteriorly to the sixth abdominal seg- 

 ment where it turns and runs anteriorly again to the first abdom- 

 uial segment; here it turns about again and joins the hind-intes- 

 tine which runs posteriorly to open on the dorsal surface of the 

 eighth abdominal segment at the vasiform orifice. The salivary 

 glands are small, nearly spherical organs, located in the dorsal 

 part of the prothorax. They are made up of a small number of 

 large secreting cells. Coming from each gland is a small duct 

 which unites with its fellows just posterior to the brain in the 

 median line. 



Muscular Syston. See Fig. 51. The muscles of the body are 

 arranged in three chief ^systems. First : the intersegmental mus- 

 cles running between the segments for the whole length of the 

 body. These muscles are attached to the folds- of the integu- 

 ment at the joints between the segments. Second : the muscles 

 of the wings, which are arranged in two sets, the elevators- and 

 the depressors. The elevators are attached at their ventral ends 

 to ridges on the integument of the ventral wall of the two poste- 

 rior thoracic segments, and at their dorsal ends to the wings. 

 The depressors of the wings are two large rriuscles situated 

 in the dorsal part of the thorax, attached to the lateral and 

 dorsal walls of the thorax, and to a deep median ventral pro- 

 longation of the dorsal integument of the thorax. Third : the 

 muscles of the legs. These muscles are in' part attached at the 

 dorsal ends to the dorsal wall of their respective segments, and in 

 part to the ventral median ridge. The ventral ends of both' sets 

 of muscles are inserted in the walls of the femur of the leg to 

 which they are attached. There is a small set of muscles for 

 moving the mouth parts, which are attached dorsally to the dor- 

 sal and lateral walls of the head and prothdtax. In the posterior 

 end of the abdomen there is a set of small muscles which move 

 the ovipositor. ' 



Nervous Si'stcm. See Fig. 51. The nervous system is very 

 much concentrated. It consists of the brain and a ventral 

 ganglionic mass. The brain is quite corriplicated althdusfh ot 

 rather small size. The cerebral hemispheres 'ai*^ v'en* promi- 

 nent, standing above the other positions of the brain. The ODtic 

 lobes are small, hidden beneath the cerebral portion of the brain. 

 The optic tracts are well' devdope 1.''' They appear as a pair of 



