38 THE LEECHES OF MINNESOTA 



Brandt, '33, found three small ganglia lying behind the jaws 

 and a nerve running along the digestive tract which he declared to 

 be the sympathetic nervous system. 



Up to this time practically all the work done on the nervous 

 system had been by surface dissection ; only the external appearance, 

 after the outer tissues had been removed, being considered. The 

 work on the inner structure then began and we find Ehrenberg, 

 Valentine, Helmholtz, Hannover, Will Bruch, Leydig, Quatrefages, 

 Faivre, and Walter contributing to the microscopic anatomy of 

 leeches. 



After Newport had discovered, between the two connecting 

 commissures in some of the arthropods, a third smaller commissure, 

 Faivre, '56, described a similar nerve, since known as the Nerve of 

 Faivre, for Hirudo medicinalis. According to his account, this 

 third commissure ran from one ganglion to the next, between the 

 two principal commissures, in many places fusing with these 

 larger cords. He made the number of nerves springing from the 

 supraoesophageal mass to be four, from the sub-oesophageal three, 

 and from the posterior at least seven. Faivre also described the 

 Leydig's cells which had been described by Leydig in 1849. He 

 found five ganglia in the head which he considered to be sympathet- 

 ic ganglia, but found no nerve connecting- them with each other, 

 or with the central nervous system, or with the visceral nerve. 



Leydig, '49, was the first to understand the follicular nature 

 of the ganglia and was also the first to describe the cells (Leydig's 

 cells) lying between the ganglionic nerves. In "Vom Ban des 

 Thiereschen Korpers" '64, he describes the head ganglia and the 

 sympatheticus, and thinks it probable that the sympathetic system 

 is joined with the central nervous system either through direct 

 connection with the brain, or through the Leydig's cells, or perhaps 

 by means of the central nerve of Faivre. 



Herman, 75, described the sympathetic system of Hirudo medi- 

 cinalis and found both the head ganglia and the gastric nerve, but 

 did not find any connection between them. He wrote, "audi ich habe 

 nie einen Zusammenhang des Sympatheticus mit den betrerl'enden 

 Ganglien oder andern Abschnitten der Bauchganglienkette gefun- 

 den, und halte, nach ihrem ausseren und inneren Bau dieses acces- 

 sorischen Gebildes, theils fur integrirende Bestandtheile des denims, 

 theils stelle ich sie in das Gebiet des IV. Gehirnnerven." When we 

 examine his figure, however, we find that he has figured ten pairs of 



