20 THE LEECHES OF MINNESOTA 



one ganglion for each somite. This chain of ganglia and connecting 

 nerve fibers are collectively cald the ventral nerve cord. From each 

 ganglion three pairs of lateral nerves radiate out to the various 

 parts of the somite. One pair of these nerves always goes to certain 

 sense organs of the somite and the others go to other definit 

 regions and organs of the somite. 



For a more detaild account of the anatomy of the nervous sys- 

 tem see Hemingway's account of the anatomy of the nervous system 

 of Placobdella pediculata, page 40. 



Reproductiv System. 



The leeches are hermafroditic. That is," both the male and the 

 female reproductiv organs are present in each individual. But the 

 two sets of organs are so related in the leech that the eggs of one 

 individual are fertilizd by the spermatozoa of another. 



The male reproductiv organs consist of a series of pairs of 

 spermaries or testes close to the nefridia in certain somites. The 

 number varies from five to eleven pairs in the different species. The 

 series on each side is connected by a common duct, cald the vas 

 deferens, which opens into a muscular tube in the neighborhood of 

 somite XI. The terminal portion of the common duct of the two 

 vasa deferentia is sometimes cald the penis. It can be protruded 

 thru the male reproductiv pore on the mid-ventral line near to or 

 on somite XII. The position is constant for a given species but 

 varies in different species. 



, The essential female organs consist of only a single pair of 

 ovaries. The ovaries usually lie in somite XI and the female re- 

 productiv opening is on the mid-ventral line one to five annuli be- 

 hind the male opening. For a detaild account of the essential and 

 accessory female organs in one species see Hemingway's account 

 of Placobdella pediculata, pages 47 to 49. 



Specific anatomical differences are noted in Part III of this re- 

 port. 



In some species fertilization may be accomplisht in a peculiar 

 way. The spermatozoa are collected in small packets, cald sperma- 

 tofores. These spermatofores are attacht to any part of the body 

 of another leech and the spermatozoa escape thru the body wall of 

 the leech into the underlying connective tissue and thence work 

 their way to the ova near the uterus, where fertilization takes place. 

 In others fertilization takes place in the uterus (or in capsules con- 



