PERICARDIAL GLAND. 
337 
life, they are alway.s paired and are best developed in the a([uatiG 
puhnonates, consisting of anteriorly directed V-shaped tubes, opening 
into the body cavity ; the cephalic or longer limbs are richly ciliated 
and directed towai-ds the Velar area, the shorter or pedal limbs being 
nnciliated and directed towards the foot; the cellular dorsally-placed 
apical sacs contain concretions and open exteriorly at the sides of 
the neck. 
In the Streptoneures these organs are formed by a mass of excretory 
cells, with numerous vacuoles containing concretions placed at each 
side of the body. At a later stage the vacuoles unite to form a 
cavity filled with a brown gTannlar mass. 
The larval kidneys have been observed in many Pelecypoda, each 
being constituted by a deeply situate ciliated canal and a more super- 
ficial part, with an external opening at the postero-ventral side of the 
cephalic region, and an internal one within the body cavity. 
The Pericardial Gland (jepl, around ; KapSia, heart) or Keber’s 
organ has an apparently important excretory function in many 
mollusks, and is a thick and spongy glandular differentiation of tlie 
pericardial epithelium covering the walls of the amides and closely 
connected with the vascular system, but always constituted by flat- 
tened cells, destitute of the concretions characterizing the renal cells. 
In the Pelecypoda it arises as a pericardial investment of the 
auricle or at the anterior angle of the pericardium, which would appear 
to be its most primitive position, and though often found as a prolifera- 
tion of the anterior pericardial walls, is not always developed at the 
same place or in exactly the same way. It is an organ quite analogous 
to the kidneys, having a rich sanguine irrigation, mainly by the 
arterial blood returning to the auricle, extracting therefrom a more 
acrid secretion than that eliminated by the kidneys, which, in 
Cardium and other marine genera, has been determined to be Hippuric 
acid; this is discharged into the pericardium and flows through the 
reno-pericardial funnels into the kidneys and thence to tlie exterior 
by the ureters. 
Except in Nucida and other archaic genera, the pericardial glands 
are almost universally present in the Pelecypoda in the form of paired 
reddish glands, upon the auricular walls witliin the pericardial cavity, 
or as an agglomeration of glandular tubules protruding from the 
anterior corner of the pericardium into the mantle lobes, both these 
forms being found among the species of our fluviatile genera. 
3 , 2 , 1900 . 
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