ON WANDERING CELLS IN ECHINODERMS. 87 
pared specimens; and others with brown or blackish pigment 
which remains undissolved, and is therefore readily seen in 
sections from hardened specimens. ‘These latter, with the 
insoluble pigment, take part in a process of wandering out 
from the body; this may happen— 
1. At any point on the free surface of the body. 
2. In the neighbourhood of the circumoral rosette feet 
(Rosetten fiisschen) and in the feet themselves. 
3. Into the tubes of the madreporite. 
Outwandering is seen occurring through the ordinary 
epidermis in fig. 8. In the oral feet Hamann has figured and 
described the presence of pigment-cells (1, taf. ii, fig./7), but 
he gives no suggestion as to the meaning of their presence. 
In young specimens only a few scattered pigment-cells leave 
the body by the madreporite—in older specimens the process 
goes on more actively ; in some cases, e. g. the specimen from 
which fig. 2 is taken, it is going on exceedingly vigorously. In 
this specimen pigment-holding cells are seen abundantly in the 
ossicular tissue of the madreporic plate and in the connective 
tissue surrounding the canals into which the water tube (“ stone 
canal”) has broken up. They are also seen amongst the 
epithelium-cells which line these tubes and the pore canals of 
the madreporite itself, whence they pass into the lumen of the 
tubes. 
From here I considered that they were carried to the 
exterior by the outward ciliary current described by Hartog 
(No. 17); but since this was originally written Ludwig (18) 
has denied that the current is outward, and he states that it 
has an inward direction. Upon this point Cuénot (4, p. 85), 
speaking of Asterids, says as follows :— 
“  T/observation des animaux vivants nous montre que le 
madreporite n’est le siége d’aucun couraut d’eau, ni pour 
Ventrée (Jourdain, Perrier, &c.) ni pour la sortie (Williams, 
Hamann)... . Enfin si l’on met une Astérie dans un bac 
rempli d’eau colorée, on voit qu'il n’en pénétre pas du tout par 
le canal de sable.” Unfortunately, from not having been near 
the sea, I have been unable to work at the point; but I think 
