1918] Bovard: Nervous Impulses in the Earthworm 113 



Methods. — (a) Dissection. All the muscle in the anesthetized 

 region was cut away after the worm had been pinned to a cork plate. 

 Owing to the fragility of the nerve, it was easily broken and in cases 

 where it was not broken it was easily impaired by stretching, so that 

 particular care had to be taken with the preparations made. Here, 

 as in the experiments discussed above, where transmission was over a 

 few segments, the coordination was good and as the nerve bridge was 

 lengthened the coordination was less complete and finally failed. Such 

 an operation must have a decided "shock" effect on the animal and 

 it does not behave as would be expected under more normal conditions, 

 consequently the length of the nerve does not represent the limits of 

 transmission, as will be shown in some experiments to be discussed 

 later. 



In all these cases it was necessary to keep the worm pinned, for if 

 allowed free creeping the anterior part would move more rapidly than 

 the posterior, the nerve was not strong enough to drag the weight of 

 the posterior part and so the nerve was promptly broken. 



In my first dissections all of the musculature in the anesthetized 

 region was removed, so that the nerve cord was the only connection 

 between the anterior and posterior parts of the worm. Later I modified 

 this so that the nerve cord, while entirely free for several segments, 

 was not allowed to touch the cork plate but was kept in its own body 

 fluids on a inece of muscle (fig. 4). All the muscle on the dorsal and 



an{. I.r n. posi: ' 



Fig. 4. Type of dissection used in nerve free preparations, (n.) nerve cord 

 with lateral roots cut (I.r.), intestine (int.) and blood vessels (d.bl.v. and v.bl.v.) 

 cut away. 



lateral walls was dissected off. The intestine was removed. This left 

 the nerve cord attached to the ventral plate of muscle. A sharp flat 

 stylet M^as introduced under the nerve cord and all the lateral roots 

 severed. A transverse cut was then made across the ventral muscle 

 so that no muscular connection remained between the two parts of the 

 worm. Wlien this type of operation was used much more uniform 



