SUBOESOPHAGEAL GANGLIA 31 



Thr Snpraoesophageal ganglia. '11 n' characters of the ganglia 

 composing the brain are hidden by the sheath of cortical cells 

 which fill up the spaces between the ganglia; the characters of 

 these can be ascertained by a study of the serial sections. The 

 median mass, the procerebrum, is formed by the fusion of the 

 procerebral lobes. Those are united before and behind, and 

 enclose a central ganglionic mass— the central body. Behind the 

 •cerebrum two pairs of fungiform bodies arise. On the anterior 

 face of the procerebrum the antennal oi- olfactory lobes which 

 represent the deutocerebrum are situated laterally. Each sends 

 a nerve (figs. 3, 8, an.n.) to the antenna. Above these and on 

 the dorsal side is a pair of lobes, the frontal lobes which are 

 contiguous with each other in the median line ; these belong- 

 morphologically to the tritocerebrum. Posterior to these in the 

 median dorsal line of the cerebrum a single median nerve, the 

 ocellar nerve (figs. 3, 8, oc.n.), arises ; this runs vertically to the 

 ocelli. A pair of lobes, which correspond to Lowne's thalami 

 of the blow-fly, are situated external to and between the frontal 

 and antennal lobes. The peduncles of the optic lobes have their 

 origins from the sides of the procerebrum. Each optic peduncle 

 (fig. 8, O.P.) contains three ganglionic masses which Hickson 

 (1885) has termed from the brain peripherally the opticon, epi- 

 opticon and periopticon (fig. 3, P.O.) respectively. 



The Suboesophageal ganglia (fig. 3, s.o.). The commissures 

 uniting the supraoesophageal ganglia to the oesophageal mass 

 carmot be recognised as such, owing to the extreme state of 

 cephalisation of the cephalic ganglia. They are represented b}' 

 the regions of the oesophageal foramen, and from the anterior 

 side of each of them arises a pharyngeal nerve (fig. 3, ph.n.). 

 From the ventral side of the suboesophageal ganglia a pair of 

 nerves, the labial nerves (fig. 3, Ib.n.), arise and run down the 

 proboscis, innervating the muscles of that organ ; on reaching 

 the oral lobes they bifurcate and branch freely, supplying the 

 numerous sense organs in those structures. The cortical cells 

 (Leydig's Punktsuhstanz), which fill up the spaces between the 

 ganglia and form an investing sheath round the whole ganglionic 

 mass, are of two kinds. The smaller cells are rounded, their 

 nuclei are large in proportion to the protoplasm, and their proto- 



