LIGIA. 79 
are the ventro-lateral pyloric lamellae. They arise on the 
ventral side immediately behind the ventro-lateral teeth. 
Their ventral edges almost meet along their whole length ; 
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-lateral lamella 
terminates in a fine point. 
The mid-gut (PI. IL, tig. 16 mid.g.) extends in a straight 
line from the posterior end of the stomach to the 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 chitinous intima. This intima is perforated 
and is shed when 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 
muscle fibres become separated by the bulging out of the 
epithelial cells. The epithelial cells of the gut are very 
large and contain correspondingly large nuclei. They 
form a syncytium, as they do not possess complete cell 
walls, but are separated by inter-cellular fibres, extending 
from the basement membrane to the intima, and probably 
of cytoplasmic origin. The 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 rows; the two 
median ventral rows of cells extend from the anterior end 
