Anafonii/ (t/id Histology of a New Eartlucorm. 67 



this action of the muscles. These sections may be circular in 

 outline, while sections from worms killed in an extended con- 

 dition are transversely elliptical. 



Within the sheath of the ventral cord, connective tissue, 

 giant fibers, nerve cells, and fibrillar nervous tissue are 

 arranged as they are in Lumbricus and AUolobophora. The 

 nerve cells occupy the lateral and ventral space within the 

 sheath, and lie in little hollows in the connective tissue, with 

 their contracted ends converging towards the points at which 

 their fibers pass into the central nervous tissue. Most of the 

 fibers from cells reach this tissue at the middle of the outside 

 of the mass, and in sections are seen in a cluster about this 

 region. Another set sends fibers into the inner ventral side of 

 each half of the fibrillar tissue. (PI. IV., Fig. 21.) The cells 

 are thickly placed along the swellings, but become less abundant 

 as the commissures are neared, and in the intervals between 

 ganglia are completely lacking for a short distance. 



The central substance of the nerve chain is seen, in cross 

 sections, as two lightly staining areas, chiefly granular or fibril- 

 lar, apparently according to the reagents through which the 

 tissue has been passed. At the center of the swellings this 

 matter fuses across the middle line below the giant fibers. 

 Elsewhere the substance of each side remains separate, with 

 the intervening space occupied by fibrous connective tissue. 



The giant fibers are three in number, as in Lumbricus and 

 AUolobophora, and occupy the same position relative to the 

 other parts of the cord as in these genera. They do not appear 

 in the subresophageal ganglion, but in the interval between 

 this and the succeeding mass the median fiber appears abruptly, 

 while the two smaller lateral fibers appear some distance 

 further to the rear. In the region of the eighth or ninth 

 somite the lateral fibers become clearly visible, but are not yet 

 half the diameter of the median fiber. At the extreme posterior 

 end of the cord the giant fibers are lacking, but beneath the 

 rectum the three are of equal size, the lateral fibers having 

 gradually increased in diameter from before backward. The 

 connective tissue completely invests the fibers which lie in the 

 ganglia in a series just within the sheath of the cord and 

 chiefly above the central nervous substance. They do not vary 



