ON WANDERING CELLS IN ECHINODERMS. 109 
described, and their ameeboid nature, it seems hardly correct to 
speak of an epithelium; they merit the expression used by 
Grobben (No. 33) in describing the ceils of the pericardial 
gland—* Die Zellen bilden kein schlossenes Epithel.” As 
regards the cells inside the membrane, they are even less regu- 
larly arranged. 
The wall of the tubules consists of a thin structureless mem- 
brane which has great extensibility, and also of fibrille. In 
some places it seems to be split into two or more lamine by 
the intrusion of the amceboid cells; in other places it is pli- 
cated, and in some cases it can be seen that plications are due 
to the presence of a moderately projecting cell which has 
pushed it up; often, as above stated, it forms the sole covering 
of the tube where there is dilatation. 
It is generally believed that the hemal system is the source 
of the amceboid cells, cells which are being lost constantly (by 
emigration, possibly also by disintegration, as Cuénot says !). 
With a view to seeing if this is truly the manufacturing place 
for new wander-cells, I have searched for nuclear divisions in 
it as well as in “ Tiedemann’s bodies.”” Specimens were care- 
fully preserved in chromic, osmic, and acetic acids, stained with 
saffranin or hematoxylin, and examined under a Powell and 
Lealand 4 inch apochromatic. The nuclei are rounded or 
oval ; most of them have a single mass of chromatin in the 
centre, from which sometimes bridles can be traced connecting 
it with the peripheral chromatin, which seems to form a sort of 
capsule for the nucleus ; in some, especially the round ones, a 
nuclear network can be more definitely made out; here and 
there one sees a more elongated and larger oval nucleus with 
two central chromatin masses ; occasionally in these and others 
there is a constriction in the middle of the length of the 
nucleus. These may be stages in the nuclear division; often 
one can see two closely approximated nuclei in the same proto- 
plasmic mass. I have not been able to make out any regular 
1 T have not observed disintegration of ameeboid cells to occur within the 
body of starfish ; he considers. that such is the source of the proteid consti- 
tuents of the “ blood-fluid ”’ (= fluid contained in perilemal spaces), 
