PAKAOOKOTOrtA AKERMANI (waUREN). 337 



series of separate alxlomiiiiil gano-lia. On tlio other hand, 

 the presence of a definitely donble nerve-cord in the thoi-ax 

 is a primitive character. 



Tlie cephalic region of the nervous system was studied by 

 means of a model made by o'lueing" together a series of cards 

 cut to shape from camera Incida drawings of serial sections 

 of a male beetle. 



The protocerebrum consists of a p:iir of procerebral lobes, 

 which in dorsal aspect are peai'-shaped, and of a pair of optic 

 gangba which are situated far forward at the anterior ends 

 of the procerebral lobes (PI. XIX, fig. 46, 'prc, op. g.). 



The deiitocerebrum consists of the antenna ry lobes ; they 

 are attached to the anterior surface of the procerebral lobes 

 immediately below the optic ganglia (fig. 47, a. I.). 



Ventrally the procerebral lobes are in wide connection with 

 a large suboesophageal ganglionic mass (fig. 47) extending 

 backwards as far as the plane of the prosternum (PI. XYIII), 



The tritocerebrnm is present as a small rounded lobe placed 

 behind the procerebral lobes, one on each side of the oeso- 

 phagus (fig. 47, tri.). A large trachea is associated with it. 



A ventral view of the cephalic system is seen in fig. 48. 

 The snboesopha.geal ganglion {suh. g.) is deeply indented in 

 front, and the roots of the mandibular (md.), maxillary {m. n). 

 and labial (/. ii.) nerves are indicated. 



The general distribution of cortex and medulla has been 

 traced in a series of sections ; but abundance of material and 

 elaborate technique would be necessary for obtaining a full 

 knowledge of the course of the various tracts. 



The optic ganglion is comparatively small, and in vertical 

 transverse section (figs. 49, 50, 51) it was seen that some of the 

 cells of the cortex are modified and perhaps degenerate in 

 character {d. c, d. n. c.) The nuclei are very small and perfectly 

 homogeneous. No cell-outlines were visible. It will be seen 

 that these small, deeply staining nuclei are clustered around 

 a small mass of medulla. The nuclei are much smaller than, 

 and have not the same structure as, those clustered in the 

 calyx of the procerebral lobes. Quite possibly this modifica- 



