ADULT HEAD KIDNEY OF BDELLOSTOMA STOUTI 863 
In fact, it is difficult to understand how a fluid in the pericardial 
cavity could escape being taken into the tubules, on account of 
the great activity of the cilia lining them, and so on into the veins. 
It is useless to speculate as to whether the head kidney forms a 
passage between the body cavity and the blood system in other 
species of the myxihoids. Weldon found clotted blood in rhe 
central duct of Bdellostoma fosteri, but thought possibly it might 
have come by way of the veias from the glomerulus. No real evi- 
dence was given in support of this hypothesis. He worked on 
complete series of sections, but says nothing about a connection 
between the central duct and the vein, although one of his dia- 
grammatic figures would seem to indicate that such a connection 
existed. 
It is quite possible that the head kidney may have some other 
function or functions than the one here suggested. But however 
this may be, it is certain that excretion can not be one of them, 
as there is no connection with ttie exterior; and since tne connec- 
tion is lost before hatching, the organ caa not fuhction in the young 
animal, as is the case with the pronephros of Petromyzon and the 
Amphibia. 
