430 



and ventral chitenous walls, uniting them both into an extremely 

 firm mass. There is also a small area of the tissue under the 

 median eye, a much larger one enclosing each lateral eye, and six or 

 seven pairs of irregular patches arranged symmetrically along the 

 dorsal wall of the abdomen, on the median margin of the six pairs 

 of entapophyses. 



In thin sections of the margin of the abdomen (fig. 1), the outer 

 cuticular layer is seen projecting inwards to form the irregular 



Fig. 1. 



chitenous network. The surface of each bar, or trabecula, is covered 

 with a very thin layer of pigmented ectoderm continuous with that 

 underlying the surface cuticula. In the older animals, the core 

 of each bar is naturally of a yellowish brown, the peripheral layers 

 like those of the surface cuticula, being colorless. The core is 

 colored a dark burnt sienna by various haematoxylin combinations, 

 but is little affected by any of the carmine stains except acetic acid 

 carmine. 



In some individuals, probably very old ones, the 

 axis of each bar is densely crowded with spindle- 

 shaped cavities or lacunae. Their long axes are parallel 

 to the long axis of the bar, and, under favorable con- 

 ditions, we can see that many of them are connected at 

 one end with a very fine tubule, or canaliculus, which 

 runs radially toward the periphery. The largest lacunae 

 are nearest the centre of the trabeculae. 



