Anatomy and Histology of a Neiv Earthworm. 59 



mass forming a gothic arch. From the expanded ventral part 

 of each commissure is given off a fourth small nerve. 



The first ventral nervous mass is depressed, and sub- 

 triangular in shape. Three large nerves arise from each side, 

 and soon meet in one large strand. Their ultimate distribution 

 has not been followed out. The ganglia posterior to the first 

 are elongated elliptical, depressed masses, with strongly convex 

 dorsal surface, and with no outward trace of division into two 

 masses. The portions of the chain between the masses are very 

 short, and show a slight median longitudinal impression as the 

 only indication of a division into two cords. As the somites 

 shorten towards the posterior end of the body, the nervous 

 masses also become less elongated, and at the same time are 

 brought closer together, the chain in the posterior part of the 

 body being finally a succession of rounded swellings, with no 

 interspaces. In the anterior somites each mass gives off from 

 near its middle two large nerves on each side. They are directed 

 forward and outward, and by large branches penetrate the 

 body-wall. Other branches given off from them doubtless sup- 

 ply the viscera. Near the anterior limit of each mass a small 

 nerve passes outward and forward on each side to the anterior 

 dissepiment of the somite in which the mass lies. Ganglia 

 forming the posterior part of the chain give off only one pair 

 of nerves. The posterior mass (possibly representing several 

 fused pairs of ganglia) gives off three pairs of nerves. From 

 its middle pass out the two ordinary nerves. Posterior to 

 these the mass becomes narrowed and gives off two small 

 nerves, which extend outward and backward. From its pos- 

 terior extremity a third pair of large nerves diverge and 

 extend backward toward the integument in the region of 

 the vent. 



The Nephkidia. 



A pair of tubular segmental organs, similar to those of 

 Lumbricus, occurs in most of the somites of the body. The 

 internal apertures of these organs are in line with the outer 

 seta3 of the inner pairs, each aperture appearing in the somite 

 preceding that in which its gland lies. The tube which 

 passes through the septum from the aperture is small at 



