GEROULD: CAUDINA. 155 
Like Kingsley, I have been unable to find in Caudina any per- 
foration at the tips of the branches of the respiratory trees, such 
as were described by Semper for other holothurians and have 
been mentioned by Sluiter (87), and Hamann (’84). Ludwig and 
other observers Lave also searched in vain for such perforations. 
In both Cucumaria and Caudina the opening and closing of 
the anus, which attend the contraction and relaxation of the muscles 
of the respiratory trees in admitting and expelling water, take 
place at quite regular intervals. 
The respiratory trees in Caudina, as in other holothurians, consist 
of the same cell layers (Plate 5, fig. 58) as constitute the wall of 
the intestine, viz. : — 
(a) A layer of flat, ciliated, peritoneal cells (¢th. ex.) with more 
irregular and sinuous outlines than those of any other of the cells 
lining the body-cavity (Plate 5, fig. 59). 
(6) A relatively thin outer layer of connective tissue (tis. cowt. 
€x.). 
(c) A layer of muscle fibers (su.), which run in all directions 
parallel to the surface of the respiratory tree. (A similar condition 
was found by Jourdan in Cucumaria Planci; whereas both Semper 
and Hamann found in Holothuria tubulosa two layers, corresponding 
to those of the intestine; 7. ¢., an inner layer of longitudinal fibers 
and an outer one of circular fibers.) The inner fibers of this muscle 
layer in Caudina have a circular direction and are more numerous 
than the outer oblique and longitudinal fibers. : 
(d) A thick inner layer of connective tissue (¢/s. cow’t. 7.), consist- 
ing of a larger proportion of the hyaline, homogeneous matrix than 
in the connective tissue of the wall of the body, and containing fine 
fibers and stellate cells. 
(¢) Aninner epithelium, which is often thrown into great folds by 
the contraction of the muscle fibers. 
8. CALCAREOUS RING. 
The term aquapharyngeal bulb has been applied by Hérouard (’89) 
to the bulb-like collection of organs suspended within the anterior 
part of the body-cavity, including the pharynx, the central portion 
of the water-vascular system and the lacunar vessels accompanying 
the central portions of the radial canals. I shall now describe the 
