PIEEADNIROLMINE THLE S, 83 
contain a fluid in which certain cells float. Some of these 
cells contain the yellow pigment which gives the animal its 
yellowish colour. Unicellular slime - glands, with longer or 
shorter ducts, which open into the surface of the integument, 
are comparatively numerous, and connective tissue cells are 
also to be met with in the parenchyma. 
The rhabdites are homogeneous refractive little rods 
which occur in most Turbellaria, and are usually found in 
great numbers either embedded in, or protruding from, the 
epidermis. They escape from the body, and often occur in 
ereat numbers in a slimy deposit the animal leaves on its 
track ; when they are expelled they leave a round hole in the 
ectoderm cells. In some species they are secreted in the 
ectoderm cells, in others, as in Mesostoma, from special cells 
beneath the integument (Fig. 57); these cells, however, arise 
from the ectoderm and remain connected with it by fine pro- 
cesses along which the rhabdites travel. 
The connective tissue cells and the rhabdite-forming cells, 
Fic. 57.—Transverse section through the pharynx of Mesostoma Hhrenbergii, 
O. Sch. After Von Graff. 
1. Mouth. 6. Yolk glands. 
2. Pharynx walls crowded with glandular 7. Testes. 
cells. 8. Nerve cord. 
3. Walls of alimentary canal. 9. Integument beneath cuticle. 
4, Salivary glands. 10. Pigment cell. 
5. Rhabdite-forming cells. 11. Dorso-ventral muscle fibres. 
with some strands of muscle fibres, constitute the paren- 
chyma. In Mesostoma this tissue is not so well developed as 
in most Turbellaria, and the spaces containing fluid are corre- 
