352 Mary R. Cravens and Harold Heath, 



divisions give rise to nerves but we have been unable to trace them 

 to their final destination. 



The dorsal, smaller fibrous core of the lateral cords is evidently 

 a, conspicuous feature in N. mirabilis as is witnessed by the following 

 comments of Vereill: "The lateral nerve trunks are very large 

 and quite inferior to the muscle layers. They are situated ventrally, 

 some distance from the edges, and near the commencement of the 

 thin-walled marginal portion of the body. In transverse sections 

 they are elliptical or rounded, with an eccentric translucent core 

 along the dorsal side, thus giving the cellular portion a thick lunate 

 or reniform shape." He makes no mention of a fibrous core among 

 the cells of the ventral part but it is most probable that it exists. 



Throughout their entire extent these lateral cords give off 

 branches whose course, in many cases, may be traced to the muscles 

 of the body wall, where they rapidly become indistinguishable. At 

 various points nerves arise from the ventral section of the cord and 

 extend inward nearly to the mid line, but in no case have we been 

 able to determine that they are actually commissural fibres. Other, 

 usually small nerves, originate in the ventral substance of the cord 

 and pass into the muscles of the ventral body wall. The lateral 

 regions of the body receive a relativly large nerve supply, especially 

 in the anterior half of the body, from the inner side of the lateral 

 cord at the junction of the dorsal and ventral fibrous bundles. In 

 this position the four or five comparativly large branches, destined 

 to innervate the cirri, take their origin. These usually soon divide 

 (Fig. 4, 18), one branch passing into the cirrus ventral to its axis 

 while the other courses dorsal to it. In this position they may be 

 followed for a considerable distance, but developing numerous 

 branches, they rapidly become distributed throughout the entire 

 extend of the cirrus, being especially abundant in its distal half. 

 The nerves arising wholly from the dorsal fibrous core of the lateral 

 cords are comparativly few in number. In several cases they dis- 

 appear in the neighborhood of the intestine and may possibly serve 

 to innervate it, although at other points it is possible to trace 

 them between the diverticula of the gut to the body wall of 

 the sides and particularly the back of the animal. From the 

 anterior borders of the brain at least 14 pairs of nerves arise, 

 and judging from their position, the more ventral ones — perhaps 

 half of the total number — connect with the ventral lobe, while 

 those more dorsally located unite with the dorsal part of the brain. 



