THE LEECHES OF MINNESOTA 37 



nerve cord which extends from the mouth to the posterior end. With 

 the exception of Haller who claimed that the leech had no nervous 

 system, no further mention is to be found until 1791 when it was 

 again described by Bibiena. In 1795 Mangili gave the correct 

 number of ventral ganglia with a good illustration of the nerve 

 cord. The supra-oesophageal ganglion, however, seems not to have 

 been known to him. In 1809 Cuvier described correctly the oe- 

 sophageal collar and its connection with the sub-oesophageal mass; 

 he gave the whole number of ganglia as twenty-three but did not 

 distinguish the posterior ganglion from the others. Like other 

 early writers he discribed the cord as single. Spix, in 1813, was the 

 first to discover the double nature of the nerve cord. He also 

 gave the correct number of nerves arising from the ventral ganglia, 

 but found only two pairs for the anterior ganglion ; the supra- 

 oesophageal ganglion was not known to him. 



Up to this time the surrounding ventral vessel had been consid- 

 ered as part of the nerve cord, but Johnson, in 1816, described it as 

 a ventral vessel. Bojanus, in his Anatomy of the Leeches, in 1817, 

 speaks of the entire independence of the nerve cord and the blood 

 system ; and Joh. Miller, '28, speaks of the ventral vessel as the 

 "eigene schwartze Haut des Markstranges." The monograph of 

 Moquin-Tandon, '27, added very little that was new to the knowl- 

 edge of the nervous system. He found that, toward either end of 

 the nerve cord, the ganglia became crowded nearer together, that 

 the two end ganglia were larger than the others, and that the caudal 

 ganglion was made up of seven or nine ventral ganglia. He con- 

 cluded from this that the caudal ganglion was not yet completely 

 formed. Weber, '28, declared the last ganglion to be a second brain 

 made up of seven knotted swellings. He writes, "Ich zahle wie 

 Bojanus, das Gehirn mit gerechnet, 22 Ganglien des Knoten 

 stranges. Aber des im Saugnapfe des Schwanzes vorhandenen 

 Ganglienstranges finde ich aus 7 verschmolzenen Knoten bestehend 

 und also einem zweiten Gehirne ahnlich .... Die 2 Faden des 

 Ganglienstranges welche die Knoten desselben unter einander 

 verbinden, verlaufen an den dem Saugnapfe des Schwanzes nahe 

 liegenden Knoten getrennt von einander. An den 7 verschmolzenen 

 Knoten dagegen, welche in der Mittelline des Saugnapfes des 

 Schwanzes befindlich sind, vereinigen sie sich. Jeden von den 

 7 verschmolzenen Knoten hat ubrigens Aehnlichkeit mit einem 

 einzelnen Knoten des Ganglienstranges." 



