DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 107 
if placed in the tissue spaces of the proboscis, are certainly 
expelled by the pore. This evidence does not of course 
demonstrate, beyond doubt, that inwardly directed currents 
never enter the pore but only gives a presumption against 
them. 
Spengel’s statement of the absence of the pore described by 
Kowalevsky and Agassiz, at the apex of the proboscis, is true 
for all the species which I have examined. 
The Heart.—As mentioned by previous observers, a large 
vesicle may be seen pulsating above the water-vessel in Tor- 
naria; such a pulsation may be observed in the dorsal side of 
the base of the proboscis in B. Kowalevskii at the stage of 
two to three gill-slits. Spengel states that this contractile sac is 
the upper of the two cavities lying above the notochord (figs. 51, 
53, &c.); this he calls the “heart.” In consideration of the 
fact (which he also admits) that it contains no blood, gives off 
no vessels, and has no muscular walls, this name seems open 
to misconstruction. As this so-called ‘‘ heart” is merely a 
space filled with loose tissue which is part of the proboscis 
gland I have preferred to call it the sac of the proboscis gland, 
and to reserve the name “heart” for the sac which lies 
between this space and the notochord (figs. 50 and 51, At.). 
That this is the actual heart can I think hardly be doubted. 
It arises at about three gill-slits as a single horizontal split in 
mesoblast between the notochord and the sac of the proboscis 
gland. It acquires muscular walls and is always nearly full of 
a coagulum similar to that which is found in the remaining 
blood-vessels of the body, which can all be traced into connec- 
tion with it. 
These peripheral vessels are (1) a longitudinal dorsal one, 
running from the heart to the tail in the dorsal mesentery 
from the back of the collar, and in the collar as a blood-space 
surrounded by the perihemal cavities (fig. 60); (2) a ventral 
longitudinal vessel running from the back of the collar to the 
tail in the ventral mesentery. These two are connected by 
blood sinuses in the skin and in the wall of the gut. I have 
uot seen the definite circular vessel which other observers state 
