104 bulletin: museum of compaeative zoology. 



meuts having been cut from either or both ends, the worms were phiced 

 in ghiss vessels partly filled with clean sand over which ran sea water. 

 In the course of two to four weeks a considerable regeneration was 

 found to have taken place at the cut ends. Two facts caused this 

 material to be abandoned. The centrosome in the giant cells was too^ 

 indefinite a structure to deal with satisfactorily, while the very limited 

 number of giant cells in a segment made the prospect of obtaining a 

 comprehensive series of conditions in the regenerative development of 

 these cells anything but encouraging. 



Hamaker ('98) demonstrated some centrosome-like structui'es in the 

 nerve cells of Nereis. I made preparations of Nereis and found some 

 veiy decided evidence of the presence of the centrosome in the cells of 

 the ventral ganglia (page 115). At the same time I examined nerve 

 cells of the earthworm, obtaining results which inspii'ed further investi- 

 gation of that material. This fact, together with the well-known regen- 

 erative power of the earthworm and the greater ease of conducting 

 regeneration experiments upon the land annelid, determined its use for 

 this work in preference to Nereis. It is, therefore, mainly with the 

 earthworm that the following work has to do. 



2. Regeneration Methods. 



The worms, AUolobophora (terrestris Savigny T) and Lumbricus agri- 

 cola HofFmeister, were easily obtained near the laboratory in Cambridge. 

 From five to ten segments were removed from the anterior end, and the 

 beheaded worms were placed in large earthen jars filled with the soil in 

 which the worms were found. The soil was first carefully examined and 

 all other worms removed. Most of the regeneration was obtained during 

 the winter or early spring months. The jars were kept in the vivarium 

 at a temperature of about 16° C. The earth was moistened from time 

 to time so that it never became dry at the surface. Many of the be- 

 headed worms burrowed a short distance below the surface, but many 

 others refused to burrow and persisted, if buried under a little eartli, in 

 returning to the surface. To protect them from the light and from 

 drying, sheets of moistened filter paper were spread over the surface of 

 the earth and the jars were covered with. glass plates. 



The cutting of the anterior end prevented feeding. In the course of a 

 few days the intestine of the worm was entirely free from earthy mate- 

 rial. The smaller worm, AUolobophora, generally burrowed beneath the 

 surface and coiled itself into an intricate close knot, remaining in that 



