THE LEECHES OF MINNESOTA 39 



nerves coming from the brain and that these include several 

 branches of the anterior sympathetic nerve, so his IV brain nerve 

 is in reality a branch of the anterior sympathetic nerve coming from 

 the oesophageal commissure at the base of nerve II. From his 

 description it would seem that he found both parts of the sympathe- 

 tic system attached to the brain at the base of the second somatic 

 nerve although that was not his interpretation. Herman also divid- 

 ed the anterior nerve packet of the ventral ganglia into "vordere 

 ventrale" and "mittlere ventrale" making the number of packets 

 seven instead of six. 



Gratiolet, '62, pointed out that the annulation had a definite 

 relation to the segmentation and made of each ventral ganglion the 

 brain, situated in the first annulus, of one of the elementary zooids 

 which go to make up the leech body. Toward the ends the zooids 

 are more closely crowded together and so the individual annulation 

 becomes indistinct or lost. Whitman, '84, made segmentation de- 

 pend wholly upon the internal organization, annulation being no 

 criterion to follow. Born, '84, based the number of somites upon 

 the number of ganglia, but did not count the number of ganglia 

 correctly. SaintLoup, '85, would go a step further than Gratiolet 

 and make the leech a colony of annulates bearing a relation to each 

 other similar to the relation of the trematodes which go to make 

 up the Tenia series. Apathy, '88, saw no ground for such a 

 colony theory, but found definite septa separating the body somites 

 (the presence of which had been denied by Born, '84) and a por- 

 tion of the coelomic cavity and a ganglion in each somite. 



Whitman, '92, proved that in Clcpsinc, the whole body is made 

 up of a series of true segments, each represented by one of the 

 separate or fused ganglia of the nerve cord. He says, "The meta- 

 meres of Clepsine show in all the important details of their external 

 features and internal organization that they represent morpho- 

 logically individuals, which have undergone internal integration by 

 which their individualities have been merged in one complex in- 

 dividuality. Each metamere has its nerve-center composed of like 

 elements, its nerves essentially identical in number, origin and dis- 

 tribution ; and its external sense organs similar in structure, position 

 and function." Whitman was the first investigator to work out the 

 relation of annulation to segmentation, in the anterior and posterior 

 regions, the morphological value of the supra-oesophageal ganglion, 

 and the relations between ganglia and somites. He, however, made 



