153 



nuclei and small stained granules. There are a 

 considerable number of masses of a light yellowish 

 pigment resembling that found in the large vis- 

 ceral ganglia cells. The fibres from the branches 

 of the alary muscles pass over and around the 

 pericardial cells to reach the dorsal vessel. From 

 their structure and situation the pericardial cells 

 appear to be of the nature of ganglion cells 

 (Fig. 32). 



The Fat-body. — The fat-body, both where it 

 occurs as a portion of the body wall and where it 

 lies as free lobulated masses, consists of cells con- 

 taining numerous oil globules. The cells are of 

 considerable size, and their borders may be fre- 

 quently traced as polygonal areas. The nuclei 

 are oval in shape with a central mass of chro- 

 matin and chromatin threads. Besides oil globules 

 the cells contain granules staining with haematein, 

 and minute droplets of a highly refractile, dark 

 substance, which gives the appearance of pigment. 

 These droplets are larger in amount in old mos- 

 quitoes than in those freshly hatched (Fig. 32). 



The Nervous System. — The ganglia of the 

 ganglionic system consist of an outer portion of 

 nerve cells and an inner portion of non-medullated 

 nerve fibres. Considerable complexity exists in 

 the larger ganglia, especially the head ganglia. 



The ganglia of the visceral system differ 

 greatly from those of the ganglionic system. The 

 ganglion cells are few in number and of large 

 size. They possess clear reticular protoplasm, a 

 little denser around the periphery than in the 

 centre. Around the inner margin of the denser peri- 

 pheral portion small stained points are arranged. 

 In the centre a variable number of granules of 

 yellowish pigment exist. 



