DIGESTION (S. S. 445) 143 



about the large central nucleus as to give rise to a beautifully regular 

 appearance simulating tessellation. As a rule, the columnar lining of the 

 intestine (fig. 11) is not very refractive. Owing to the low visibility of 

 this lining, and the difficulty of seeing through the mass of granules con- 

 tained in the intestinal cells, the lumen is usually hard to decipher; to- 

 ward the anus, however, it may become more distinctly visible. Occasion- 

 ally, the granules are so few or so transparent that the contents of the 

 intestine can be seen with ease, but this is rather exceptional. 



Granules. The structure and arrangement of the granules in the 

 intestinal cells of Mononchus lacustris may be taken as somewhat typical. 

 The granules of this species are numerous and packed rather closely in 

 the cells, and give rise to a more or less distinct tessellation. Specimens 

 fixed with Flemming solution, and mounted in glycerine jelly, show many 

 of the granules as refractive shells, enclosing a relatively large inner 

 spherical mass, which appears dark or light according to the nature of 

 the focus of the microscope. This structure is characteristic of some of 

 the smallest, as well as some of the largest, granules. These appearances 

 are not uniform throughout the intestine, the shell-like structures being 

 more apparent in the posterior part than elsewhere, and less apparent 

 through the middle portion of the body, where the granules are largest 

 and most abundant. 



These intestinal granules play an important role in the economy of 

 the nema some of them are in fact indispensable intracellular organs. 

 Little as we know about their functions in detail, it is 

 already certain that they have to do not only with the ,,_, 

 secretion of various digestive fluids, but also with the 

 transformation and storage of the digested matter. The \| c // ^ 

 granules in any given cell may be of several kinds, doubt- 

 less serving entirely different functions. These facts 

 the author has demonstrated by intra-vitam staining. 



Digestion 



Food Remnants. The digestive fluids of the mon- 

 onch must be well fitted for dissolving ceratin, suppos- 

 edly the main component of nematode cuticle, for the 

 cuticle, as well as most other parts of the ingested victim, 

 disappears completely in the course of digestion. The parts that resist 

 digestion longest are the spicula of male nemas and the oral spears of the 

 spear-bearing sorts. These organs, the spicula and the spear, are com- 

 posed of relatively thick layers of solid "ceratin," and furthermore are 

 protected from the action of the digestive fluids because of their situation 

 in the interior of the ingested nema, and hence are among the last to be 

 dissolved. Such an undigested remnant, a spear or a spiculum, consti- 



