THE STRUCTURE AND AFFINITIES OF HERDMANIA CLAVIFORMIS. 245 



the reader may suspect he sees nerve-branches comparable to those reported by 

 Kowalevsky ('74) in Distaplia and Phallusia. I can, however, find little to support 

 this view. They are wholly fibreless; they end abruptly without reaching a length 

 to make them of any consequence as nerves; they do not run to any organ or tissue; 

 and they are wholly median and unpaired. While I can see no reason for regarding 

 them as abortive nerve-roots, I have no alternative suggestion as to their significance. 

 The lumen of the duct undoubtedly extends into some of them, as shown in Figure 

 16; and I have tried to find it communicating with the rapheal blood-sinus, but have 

 not been successful. 



8. The Digestive System. — The intestine is in the form of an extremely long, 

 straight, narrow loop. A rather pronounced constriction marks the junction of the 

 thorax and intestine, but from this point on to its end the loop holds a very uniform 

 size. The oesophagus constitutes almost the whole of the ventral limb of the loop, 

 the stomach being situated far back. The portion of the loop behind the stomach 

 is about one and one-half times the length of the stomach. The ascending limb of 

 the loop, the intestine proper, is considerably thicker than the oesophagus. A dis- 

 tinct constriction at the bend in the loop marks off what may be called a duodenal 

 section of the intestine. This is much smaller at its gastric end, the pyloric opening 

 of the stomach being, as is likewise the oesophageal opening, much smaller than the 

 parts of the digestive tube to which they respectively belong (PI. XVIII, Fig. 2). 



The oesophagus becomes strongly compressed laterally as it approaches the 

 stomach, so that its cross-section is a narrow ellipse. That this compression is a 

 structural matter and not due to collapse merely is proved by the fact that along 

 the dorsal edge the epithelial wall falls away abruptly to about half its normal thick- 

 ness. The relation of this edge to the stomach wall, to be described presently, is 

 also evidence of its constancy. 



The stomach is a well-defined organ. It has the general form of a barrel. Its 

 length is approximately once and a half its thickness. Its wall is thrown into seven 

 prominent, nearly equal folds which extend its entire length, and an eighth much 

 smaller one which usually does not reach quite to the posterior end. These folds are 

 arranged as follows: on the side next the rectum there is an area of plain wall of 

 somewhat less than one-third the entire circumference of the organ. The seven large 

 folds are distributed nearly uniformly over the remaining two-thirds of the wall. 

 The small eighth fold is situated between the second and third large folds counting 

 from the foldless area on the dorsal side (PI. XVIII, Fig. 7). The small fold is con- 

 sequently somewhat to the right of the dorsal fine of the stomach. This small fold 

 is in direct continuation at its oesophageal end with the narrow dorsal edge of the 



