110 HERBERT E. DURHAM. 
karyomitosis ; the nuclei are small, which makes the matter a 
difficult one to investigate. 
Prouho considers that the dorsal organ is the seat of “ une 
production constante des éléments figurés, destinés a remplacer 
ceux qui ont cessé de vivre dans les fluides nourriciers de V’in- 
dividu” (‘ Compt. Rend.,’ cii, 1886, pp. 1403-6). 
The remaining parts of the hemal system are similar in 
structure, but with the exception of the gastric tracts they do 
not consist of actually separate anastomosing tubes. 
Sections of the gastric hemal strands are very similar to 
those of the dorsal organ; the spheruliferous corpuscles are 
much more abundant, however, than they are in that structure. 
They are not necessarily identical with those that leave the 
body through the dermal branchiz (26) (cf. the two similar 
forms of corpuscle in Echinus sphera), but the pigmenta- 
tion in the forms I have investigated is too slight to make any 
distinction from their appearance. Their presence suggests 
that they may play some part in the absorption of food material 
(ef. the fat absorption question in Vertebrates), and possibly 
also its subsequent distribution to the tissues. Sections of 
young specimens of A. rubens (2 mm.) prepared with osmic 
acid show wander-cells containing globules and granules which 
stain black, and which resemble the globules and granules of 
food material in the gut-wall. Such ameeboid cells are espe- 
cially to be seen in the dorsal organ and in the radial hemal 
strands. This appearance suggests that they travel along the 
hzemal strands to minister to the nutrition of the tissues; in 
development it has been abundantly shown, in other animals, 
that leucocytes are used in the nutrition, not only for purposes 
of construction but also of destruction (vide 39). 
Over and above the function of producing new leucocytes 
(or pigment) that the hemal system may have, the following 
considerations render it probable that it assists in carrying on 
the nutrition of the animal:—(1) It contains a highly albu- 
minous fluid; (2) it is in connection with the gut on the one 
hand, and with various organs of the body on the other, of 
which we may mention the generative organs, perhaps, as 
