rand: nervous system of lumbrigid^. 105 



condition, unless disturbed, as loug as it was kept, — five or six weeks. 

 The larger earthworm, Lumbricus, which generally remained on the 

 surface, was always found stretched out when the earth was exposed for 

 moistening. 



An attempt was made to keep some worms during regeneration in 

 glass vessels containing moist filter paper, instead of in earth ; but the 

 method was more troublesome and possessed no advantages over the 

 other. Unless the paper was changed every day or two, the worms were 

 likely to die, while of those kept in the earth only about ten per cent 

 died during regeneration. 



Worms were killed after from seven to forty days subsequent to the 

 operation. In Allolobophora, the light-colored conical bud that marked 

 the regenerated segments was usually to be seen in two or three weeks 

 after the operation of cutting. Lumbricus regenerated much more 

 slowly. All of the preparations which I shall discuss are from indi- 

 viduals of Allolobophora. 



Eegeueration of posterior ends was also obtained, but little was done 

 upon that material. The anterior ends have the advantage that the 

 regeneration of both the brain and ventral nerve-cord can be observed. 



When the desired period of regeneration had elapsed, the worms 

 were dropped into fresh water for a moment to remove the clinging 

 earth. The anterior end, including some six to twelve of the old seg- 

 ments, was clipped off with scissors and the fragment bearing the 

 regenerated part was at once dropped into the fixing fluid. Stupefac- 

 tion, where such small fragments were to be fixed, was found to be of 

 no advantage. 



In the less advanced stages of regeneration the inability to feed made 

 unnecessary the cleaning out of the intestine before fixing. In some 

 of the more advanced stages feeding had been resumed and the worms 

 had to be kept upon moist linen for a day or two until the anterior 

 part of the intestine had become clean. 



3. Fixing Fluids. 



The best fixing fluid for general purposes was found to be Flera- 

 ming's stronger chromic-osmic-acetic mixture. This fluid not only gave 

 the best fixation of the old ganglion cells, hut also gave by far the most 

 satisfactory fixation of mitotic cells. Some of the best demonstrations 

 of the exceedingly fine radiating fibrillte in the ganglion cells were ob- 

 tained by this method, and the achromatic fibres of the mitotic figure 

 were very sharply brought out. 



