34 PHYSIOLOGICAL SERIES. 



so, and a variety of stages of concentration occur within the 

 Order. In the embryo the nervous system is usually entirely 

 unconcentrated, and the adult condition is attained by the >uc- 

 cessive fusion of ganglia in the embryonic and pupal >tages. 

 Some embryos, however, have a single onsegmented po-t-oral 

 mass, from which the ganglia of the adult are produced by 

 subsequent segmentation. 



D. 27. Models of the brain (cerebral ganglion) and right fun<ii- 

 form body of a Black-beetle (Periplaneta orientalis) x (JO, 

 with a drawing of a transverse section through the left 

 half of the ganglion, the position of which is indicated 

 by a black line on the model. The cerebral ganglion 

 in Insects consists to a large extent of a pair of proto- 

 cerebral lobes in connection with the optic ganglia ; 

 thus the size of the brain depends mainly upon the 

 degree of development of the eyes, and need not 

 necessarily afford an indication of the state of intelligence 

 of the individual. The brain further comprises a second 

 pair of centres (deutocerebrum) , probably olfactory, in 

 connection with the antennae; and a third pair (trito- 

 cerebrum), situated in the roots of the circamoesophageal 

 connectives, that innervates the labium and gives rise to 

 the visceral system. It apparently corresponds to the 

 oesophageal ganglia of Crustaceans. 



The protocerebrum consists of the optic ganglia (not 

 shown in the model) and of a pair of large protooerebral 

 lobes, contiguous in the mid-line. The latter are united by 

 commissures, and each contains several remarkable struc- 

 tures. The most striking of these are the fungifonn bodies 

 organs that are possibly indicated in Crustacea, but 

 reach their full and characteristic development in Insects. 

 One is lodged in each protocerebral lohe; it consists of 

 two masses of dense neuropile (calyces, F) deeply concave 

 from side to side, and -ituated near the dor.-al -urfacf of 

 the brain with their concavities facing upwards. (The 

 calyces are exposed on the right side of the model.) Their 

 neuropile derive- it- fibre- from a caj of ganglionic nuclei 

 (coloured yellow). Each calyx gives off from its lower 

 (convex) surface a short pedicle, that unites with its fellow 



