AIntFIG 3: Transmission electron micrographs (TEMs) of young and old C. elegans showing accumulation of bacteria in the intestine near the pharyngeal valve.

A&B. Lengthwise views of pharynx and anterior intestine. (White arrowheads) lumen of the pharyngeal-intestinal valve, (brackets) cytoplasm width in older worm.
A. In a young adult specimen, the lumen is filled by the mushy remains of bacteria that were ground into small bits by the pharynx. The pharyngeal valve is seemingly closed and the intestinal cells have a rich complex cytoplasm containing a variety of different organelles. The intestinal lumen is lined by a distinctive brush border of villi. (Image source: N533 [Hall] J2 F301.)
B. 7-day-old class B animal showing intestinal lumen that is hugely swollen by intact bacteria which are not becoming digested but instead are multiplying there. The pharyngeal valve is seemingly forced open by the accumulation of too many bacteria and the cytoplasm appears squashed to a minimum width (brackets) by the swelling of the lumen, but is still represented as a chain of empty white vacuoles. The brush border of villi is no longer evident at the edge of the lumen. (Image source: N824 [Hall] 4927.)

Click on picture for full resolution image.