15 



are the veiitro-lateial pyloiic lamellae. Tliey arise on the 

 ventral side immediately behind the ventro-lateral teeth. 

 Their ventral edges almost meet along their whole h-ngth ; 

 their lateral edges extend in an oblique direction from 

 behind the dorsal lamella to the ventral side at the anterior 

 end of the mid-gut, where each ventro-lateial lamella 

 terminates in a fine point. 



The mid-gut (PI. II., tig. 16 iiiid.fj.) extends in a straight 

 line from the posterior end of the stomach to tlie rectum 

 in the posterior region of the abdomen. It is of uniform 

 width throughout, except at the posterior end, where it 

 narrows considerably, and is surrounded by a sphincter 

 muscle. Three regions can be roughly made out, the 

 arrangement of the epithelial cells of the gut being the 

 means of demarcation. The wall is composed of three 

 layers, an outer muscular layer, a median basement 

 membrane, and internally the epithelium, which is 

 covered by a chitiuous intima. This intinia is perforated 

 and is shed Avhen the animal moults. The muscular layer 

 is composed of two sets of muscles, an outer longitudinal 

 and an inner circular layer, but this only applies strictly 

 to the anterior end of the mid-gut ; further back the 

 mus(de hbres become separated by the bulging out of the 

 epithelial cells. The epithelial cells of the gut are very 

 large and contain correspondingly large nu(dei. They 

 form a syncytium, as they do not possess complete cell 

 walls, but are se})arated by inter-cellular hbres, extending 

 fi-om the basement membrane to the intima, and probably 

 of cytoplasmic origin, 'ilie arrangement of the epithelial 

 cells varies in different regions of the mid-gut. In the 

 anterior region, which is almost half the entire length of 

 the mid-gut, the cells are irregularly arranged. On the 

 lateral sides they extend in longitudinal lows; the two 

 median ventral rows of cells extend from the anterior end 



