616 SERGIUS MORGULIS 



that segment. Locomotion is, accordingly, accomplished through 

 the alternation of passive extensions and active contractions of 

 successive segments. 



To me it appears that, while in its wide aspects Friedlander's 

 analysis is perfectly correct, it becomes, when applied to idivid- 

 ual segments, a matter of inference rather than of direct observ- 

 ation. Although I have repeated some of Friedlander's experi- 

 ments, and confirmed practically all his statements, I have failed 

 to convince myself that his hypothesis is correct. On the con- 

 trary, every observation has strengthened my opinion that the 

 locomotion of the earthworm is reducible to the reaction not of 

 single segments, but of whole groups of segments. 



This can be readily demonstrated by the simple experiment of 

 cutting a worm in two, and stitching the anterior and posterior 

 pieces together with a fine silk thread. The anterior piece, 

 crawling on a flat surface, tugs along the posterior piece, and both 

 move by strictly coordinated movements as though they were 

 not detached. If the tension of the thread connecting the two 

 pieces is relaxed, however — as is the case, for instance, when the 

 anterior piece changes its course — the movements of the pos- 

 terior piece stop at once. This clearly proves that the reaction 

 of the posterior piece is caused by the pull exerted on it by the 

 anterior one. Now, when the posterior piece is being tugged, 

 a part of it, comprising six or even more segments, is at first 

 drawn out; after a certain limit of elongation has been reached, 

 a vigorous contraction of the longitudinal muscles pulls the re- 

 maining segments forward. In the remaining segments the proc- 

 ess observed in the first will thereupon be precisely repeated. 



Other experiments were likewise performed where, instead of 

 stitching the anterior and posterior parts of a worm together, 

 pieces of the nerve cord alone were removed. The method of 

 operating was different from that used by Friedlander, who was 

 obliged to cut the worm open to get at a particular portion of the 

 nervous system. In my own work such operations were accom- 

 plished with the least possible injury to the body-wall of the ani- 

 mal, by pulling out the nerve cord. For this purpose the worm 

 was first stupefied and a ventral incision was then made extend- 



