192 
EDWIX 8. (JUODKICH. 
clue to theoretical bias. It is true that I hold that the renal 
organ of Aiuphioxus is a nephridiuin homologous with the 
nephridia of Annelids and Platyhelmiuths, and not homo- 
logous with the kidney tubules of the Craniata (5, 7) ; but it 
is now well known that the true nephridia of Annelids may 
open into the coelom. There is no a priori reason why 
they should not do so in Amphioxus. However, no nephri- 
dium has yet been found possessing both solenocytes and an 
internal opening, though such intermediate stages must pre- 
sumably have existed. 
The Relation of the Nephridium to the Blood- 
supply. — The general blood-supply has been well described 
and figured by Boveri ( 1 ). But according to my observa- 
tions the vessels occur not so much as narrow capillaries, as 
in the form of a large expanded vessel spreading over the 
area occupied by the excretory organ. This is shown in 
sections (figs. 7, 23), and also in the reconstructions given on 
Plate 11. It will, moreover, be noticed that, although the 
greater part of the bloodvessel lies on the inner or atrial 
surface of tin; nephridium, yet several loops pass round to 
the outer or coelomic surface. Thus a considerable part of 
the nephridial canal is entirely surrounded by the blood- 
vessels. The solenocytes radiate out from the canal, and 
always lie on the wall of a bloodvessel, being attached to it 
by a })rotoplasmic process (tigs. 4, 15). 'I’he way in which 
these cells are distributed is shown iu figs. 14, 19, and 
diagrams 2 and 3, and the text-figure. It will there be seen 
that the longer tubes, which are of course those belonging to 
cells furthest away from the canal, pass over the shorter 
tubes to reach their destination. Never do the solenocytes 
project freely into the ccclom ; when they appear to do so in 
sections this is, I believe, due to the cell having become 
detached accidentally, either during the process of preserva- 
tion or of cutting. The tubes are therefore fixed at both 
cuds. 
In the text-figure may also be seen the peculiar disposition 
of the solenocytes at the top of the secondary gill-bar. Here 
