MUSCLES AND VISCERA OF THE IMAGO. 229 



The thoracic ganglion appears to represent functionally the 

 medulla oblongata and spinal cord of vertebrates. Its destruc- 

 tion causes instant death, whilst a fly from which the head has 

 been removed behaves very much as a vertebrate does after the 

 removal of the cerebral hemispheres. It is worthy of remark 

 that the great nerves to the halteres, which also supply the 

 chordotonal organs of the thorax, are connected with the 

 thoracic nerve-centre, just as the auditory nerves of vertebrates 

 are with the medulla oblongata. 



The organs of the special senses and the complex sexual 

 apparatus cannot be considered in this part of my work, as it 

 will be necessary to give full details of their structure and 

 development to justify the views I hold, and a brief account of 

 these parts would be practically without value. 



THE I'EMAI.K liLOW-lXY {CalUpliora Etytlirocepliala). 



