1918] Bovard: Nervous Impulses in the Earthworm 129 



ceeds. The giant fibers have little to do with locomotion and are 

 specialized for rapid, end to end contractions. 



The excellent work of Krawany (1905) on the neurones of the 

 central system of the worm and the researches of Dechant (1906) on 

 the peripheral nervous system, together with the great amount of 

 work done by the older writers, such as Bethe (1903), Rhode (1887), 

 Apathy (1897), Retzius (1900), Biedermann (1904), Smirnow (1894), 

 and others, have demonstrated that the nervous system is compounded 

 of many short neurones. The longest elements are some few large 

 fibers from the anterior end of the cord which arise in the sub- 

 esophageal ganglion and run posteriorly to the terminal segment, but 

 Krawany (1905) shows that for the most part the other nerve fibers 

 run only from one ganglion to the next. 



Sensory nerve fibers originating in the epidermis pass down 

 through the main nerve trunks to the ganglion where they branch as 

 T- or Y-shaped bifurcations immediately on entering. These run but 

 short distances before ending in fine arborizations. Krawany (1905) 

 was unable to demonstrate that these passed into ganglia anterior or 

 posterior to the segments of entrance, but was inclined to think that 

 they remained within the ganglion entered. No demonstration of 

 neuro-muscular end organs has ever been made in the smooth muscle 

 of earthworms. Retzius (1895) and Langdon (1900) have shown, by 

 using Golgi methods, that nerve fibers are in among the muscle cells, 

 but Dechant (1906) by using methylene blue was unable to differ- 

 entiate any definite end organs. Many nerve fibers parallel to muscle 

 can be seen, showing the presence of abundant nervous tissue, but all 

 fibers which looked like end organs proved to run only short distances 

 and could not therefore be true nerves. "While free sensory endings 

 in the subepithelial regions are not yet demonstrated, Dechant believes 

 they are undoubtedly there. 



After entering the cord the sensory nerves bifurcate, one branch 

 passing up and another down the cord on the same side as they enter. 

 They may then form synapses with neurones of motor ganglia in the 

 anterior, middle, or posterior groups of nerve cells. These large cells 

 send out neuraxes which may or may not cross to the opposite side, 

 where they leave by one of the three lateral roots. 



Within the cord, however, there are still other paths open to 

 impulses entering by the sensory paths. The large multipolar cells are 

 the association cells which show an arrangement into three groups, an 

 anterior, a middle, and a posterior group. Their function is to connect 



