INTERNAL ORGANS. 93 



the same. Instead of being almost equally dis- 

 tributed in every segment of the body, the greater 

 proportion of it is removed forward and concen- 

 trated in the head and thorax ; the principal 

 changes are the following : the brain increases 

 steadily in size, the little ganglion beneath the 

 oesophagus approaches it as closely as the atten- 

 uating oesophagus allows, the cords which con- 

 nect it with the first body -ganglion shorten, then 

 broaden so as to obliterate the former, and finally 

 lengthen so as to separate the two by more than 

 their f ormer distance ; the first and second ganglia 

 of the body approach each other until they fair- 

 ly melt in one, the connecting cords becoming 

 more and more divergent and then approximat- 

 ing until they, too, merge in the general mass ; 

 the third and fourth, that is, the last thoracic 

 and first abdominal ganglia, act in a similar way 

 toward each other, and at the same time approach 

 the united first and second until they are sepa- 

 rated only by short and thick commissures, and 

 together form a thoracic mass, nearly equal to 

 that of the head ; it will be noticed that one of 

 the abdominal ganglia has, therefore, entered the 

 thorax. With the shortening body of the insect, 

 the ganglia behind in like manner approach each 

 other, the uniting cords not diverging but becom- 

 ing sinuate, and regaining their former straight- 

 ness only after most of the changes incident to 



