108 ASYMMETRY OF THE NEMATODE 



elements composing the net. There were about five of these refractive places 

 between the second and third tubercles, four between the third and fourth, two 

 between the fourth and fifth, and fifth and sixth, these numbers corresponding to 

 the increasing coarseness of the tessellation on the posterior part of the neck. 



The third tubercle had the form of a truncated cone. It was a little higher 

 than the second, and the sides of the cone .were somewhat steeper. It had a chi- 

 tinous cap like that of the second tubercle but truncated, and the outer surface 

 of this cap bore on its margin exceedingly minute, round, flatish sub-tubercles 

 perhaps four only so arranged that in optical section the middle of the face 

 of the tubercle appeared almost imperceptibly depressed. The chitinous cap 

 was also hollowed on its inner concave face, the depth of the excavation being 

 about three-fifths the entire depth of the cap. This tubercle was also columnar 

 in structure, the number of elements appearing in the optical section being 

 slightly greater than in number two, perhaps 12. Tubercle number four was 

 shaped very much like number three, but was a little more rounded on its exterior 

 surface, so that the entire tubercle in optical section presented a rounded contour ; 

 its cap being about as thin as that of number three, but extending farther over 

 the surface of the tubercle, extending in fact, nearly to the general body surface. 

 The internal structure was like that in numbers two and three, except that the 

 number of elements was slightly greater, and the outer elements were spread 

 apart as they extended outward, so that the striation appeared somewhat fan- 

 shaped. This fourth tubercle stood half way between the median and cardiac 

 bulbs, and its surface bore the same kind of minute subsidiary surface tubercles 

 as were noted on the third. The number of these subsidiary tubercles was slightly 

 greater on the fourth than on the third; there appeared to be at least five or six 

 of them. The fifth tubercle was very much like the fourth, but slightly smaller, 

 and also bore the minute subsidiary surface tubercles mentioned in connection 

 with the third and fourth, but fewer of them, in fact there was perhaps only one. 

 The sixth tubercle was somewhat asymmetrical in optical section, wider than 

 any of the preceding, and composed of a greater number of elements. Its chi- 

 tinous cap was slightly thinner than that of number five, just as that of number 

 five was slightly thinner than that of number four. This tubercle was located 

 opposite the anterior portion of the intestine. It remained uncertain whether 

 this sixth tubercle bore any of the minute subsidiary surface tubercles. The 

 columnar structure of the third, fourth and fifth tubercles, especially the two 

 former, did not appear to be absolutely uniform, and it seemed likely that this 

 lack of uniformity was due to the optical effect of special elements passing radi- 

 ally through the tubercle to the minute subtuberclcs, and suggested the possi- 

 bility of the presence in the tubercles of nerve elements connected with the small 

 subsidiary tubercles. From the sixth onward the tubercles were of varying size, 

 sometimes a little smaller than number five, sometimes as large as number six, 

 the six or seven along the middle portion of the body tending to be smaller, and 

 two or three in the proximity of the spicula tending to be larger. The chitinous 

 caps were less pronounced through the middle of the body and, on account of 

 their retractive properties, appeared merely as an accentuated contour; that is 

 to say, when seen in exact optical longitudinal section the chitinous covering 

 gave rise to a sharp dark contour, which contrasted strongly with the contour pro- 

 duced by the corresponding portion of the somatic cuticle between the tubercles. 



