ASCARIS LUMBRICOIDES LINN^US 83 



taneously, expansion is due to the elasticity of the cuticle. 

 Besides the longitudinal muscles there are several special muscles 

 in Ascaris, which will be considered in connection with other 

 organs. 



Digestive system. The digestive system of Ascaris is 

 very simple and consists of a straight tube running from the 

 mouth to the anus. It may be divided into three sections: 

 the oesophagus or foregut, the intestine or midgut and the 

 rectum or hindgut. The (esophagus is short and shows a tri- 

 radial lumen in cross-section. Being a stomadeum it is naturally 

 lined with a heavy cuticle. The wall of the oesophagus is formed 

 by myo-epithelial cells of special structure. Their fibres, ar- 

 ranged radially, form real dilatator es oesophagi, i. e., they widen 

 the lumen, while the cuticle lining serves as their antagonist. 

 A few gland cells are found in the wall of the oesophagus com- 

 pletely inclosed by the myo-epithelial cells. The intestine or 

 midgut is a straight canal which is so much flattened dorso- 

 ventrally that it almost has the appearance of a band; its wall 

 is composed of high, columnal epithelium. Two enormous muscle 

 cells form a network of fibres around the hind end of the intes- 

 tine and act as dilatatores. The same two cells furnish in the 

 male also the muscular fibre-net of the ejaculatory duct. The 

 short rectum is lined with a cuticle and is surrounded by a ring 

 of six large gland cells. The position of the anus has been de- 

 scribed above. 



Excretory system. The excretory system is inclosed in 

 the side lines. The side line appears as a heavy ridge separating 

 the longitudinal muscles. Already with naked eye one can 

 observe a longitudinal line dividing the side line into two lines, 

 and this division appears still clearer in a cross-section. The 

 structure of a side line is quite complicated and is composed of 

 various elements of which the subcuticle is the least conspicuous, 

 being in the side lines no more developed than in other regions 

 of the body wall. The main tissue of the side line is divided 

 into upper and lower symmetric halves by the cells of the 



