ON WANDERING CELLS IN ECHINODERMS. 107 
very hard to see: the surface of the gastric hemal strands is 
more thoroughly ciliated than that of the dorsal organ, but 
even here the difference is very great between its surface and 
that of the coelomic epithelium, for instance. Cuénot (4) 
mentions that there is slight movement about the dorsal organ, 
but goes no further into the question. By dissection (fig. 4) or 
by sections the different strands are seen to anastomose with 
one another: each is tubular in structure, the walls of the 
tube being constituted of a fine extensible and elastic mem- 
brane with the longitudinal fibrils mentioned above; in parts 
this tubular nature is shown clearly where the contained fluid 
is more abundant. These have been already referred to as 
transparent swellings ; their surface may be perfectly free from 
cells, or there may be a few cells forming a reticulum over the 
surface by means of their processes (fig. 5), or the cells may be 
flattened out and form a complete covering. 
The fluid gives a granular coagulum with reagents which 
precipitate proteids (alcohol, picric acid, &c.), showing that it 
contains a considerable amount of these substances. The dila- 
tations seem to be parts where this nutrient fluid is tempo- 
rarily more abundant; I have always seen them even when the 
greatest care has been taken in exposing the organ to prevent 
injury. In sections similar coagulum is seen in varying 
amounts in non-dilated tubes. The highly albuminous nature 
of the fluid no doubt led Ludwig, &c., to regard it as the 
nutrient fluid, and therefore worthy of the appellation “ blood.” 
Cuénot, on the other hand, considers that the perihemal canals 
contain the true blood-fluid. My sections show a very slight 
amount of coagulum in these spaces, often none at all. He 
regards the dilatations (p. 90) as “ places predisposed for the 
exit of lymph-cells ;” my observations lead me to think that at 
these points the migration of cells from the gland is least 
active. Speaking of the “epithelium,” he says, ‘ Mais il 
manque dans tous les endroits de sortie,” a matter which 
we have mentioned above. Vogt and Jung (No. 6, p. 610) 
describe these dilated tubes as “ grosse vollkommen homogene 
und durchsichtige Blaschen welche sich mit Beale’s Carmin 
