KESAL ORGANS OK NEPHllIDIA. 
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Mr. L. E. A<1 aiiis has roL-eutly observed that, on tlie sandliills at 
Sandwich, //e//j- airtusidua is cliieliy found upon the Hound’s 
Tongue (Cijnogloi^sum officiiDde), clinging to the witliered steins and 
so closely simulating the clusters of burr-like seeds that it is difficult 
to distinguish the shells in the sunlight. 
Limiiau’ when crawling on the bed of a stream or pond assimilate 
in a remarkable way to their surroundings, and the darkly mottled 
mantle which often shows dimly through the shell does not render 
them more perceptible, but rather tends to their closer approximation 
with tbe appearance of their surroundings. 
The \"lvlj)ar/a(f are often found so thickly coated with mud that 
no portion of the actual shell can be seen, and the resemblance to, 
and assimilation with, tlie bed of the canal or river is complete. This 
incrustation olten contains fragments of plant tissues and may also 
be rich in Alg(t', chietly represented by numerous species of Diatoms. 
OscUlatur'uc are sometimes eipially plentiful in the deposit and 
impiently, in the living condition, imparting a greenish tint thereto. 
Amongst bivalves tbe tufacoous or muddy deposit upon the pro- 
truding posterior part of the valves is well known to all conchologists, 
who readily acknowledge the i>erfection of the disguise, which is only 
penetrated by the opening of the valves and the protrusion of the 
siidions. Often this incrustation becomes the seat of growth for 
Ahjic or other water plants, and the difficulty of detection is corres- 
pondingly increased. 
'I'he A'epiikidia kidney), Kenal organs or Kidneys, known 
in Oastroi)ods also as the Precordial gland, are typically paired and 
dor.sally placed excretory organs, always .symmetrical in .symmetrically 
organized animals with paired gills, and metameric in Ndiitilus, 
in which the respiratory organs have a serial character, but single in 
most Gastropods in correlation with the loss of the moities of many 
other of their primitively paired organs. 
These organs in the mollusca assume a variety of forms in exotic 
genera or the constituent parts may jiermeate amongst the various 
organs of the body; usually, however, they consi.st of a pair of tubules, 
each of which is closely folded upon itself, forming a looj), connected 
proximally by the ciliated reno-pericardial funnel with the base of 
the pericardial cavity or secajndary ccjclom, with which they are always 
in intimate relation. The proximal tract or limb is enlarged and 
sacculate with rich vascularization and constituted by browni.sh or 
