236 



COCKROACHES. PHYLUM ARTHROPODA 



probably in some sort of symbiotic relationship with the insect. 

 The blood resembles that of the crayfish but, as might be expected 

 in view of the mode of respiration, contains no respiratory 

 pigment. 



NERVOUS SYSTEM AND SENSE ORGANS 



The nervous system (Fig. 173) is on the same general plan as 

 that of the crayfish. It comprises a pair of supra-oesophageal 

 ganglia, which receive optic and antennar}^ nerves, a pair of 

 short, wide circumoesophageal commissures, a suboesophageal 



ganglion, and a double ventral cord 

 with a ganglion in each of the first 

 nine segments behind the head. In many 

 insects, especially the Hymenoptera 

 (p. 260), the supra-oesophageal ganglia, 

 which represent three pairs of ganglia 

 fused together, are highly developed and 

 deserve the name brain. The alimentary 

 '/-y canal is supplied by a visceral nervous 

 system which receives nerves from the 

 circumoesophageal commissures and 

 the brain. Its principal ganglion lies 

 on the upper side of the crop. The 

 sense organs include the large compound 

 eyes, which resemble those of the 

 crayfish in structure, the antennae, which 

 are tactile and olfactory, the labial and 

 maxillary palps, which are gustatory and olfactory, and anal 

 cerci, which are tactile and also sensitive to sound vibrations, 

 various sensory bristles, and possibly a pair of oval white patches 

 which are found above the bases of the antennae and are known 

 as the fenestrae. 



ORGANS OF REPRODUCTION 



The sexes are separate. The testes (Fig. 174) are small, paired 

 organs, embedded in the fat body below the fifth and sixth 

 abdominal terga. In the adult the testes are no longer functional. 

 Two vasa deferentia lead backwards and downwards from them 

 to the seminal vesicles, which are beset with short finger-like 

 processes and lie side by side to form the so-called mushroom- 



Fig. 172. — A section 

 through a lobe of the 

 fat body of a cock- 

 roach X 650. — From 

 Imms. 



e. Excretory cell with concre- 

 tions ; /., fat cell ; m.. cell 

 containing bactetia. 



