216 LECTURES ON 



from its own burrow. First it closes in the enormous gape, that 

 capacious portal for the egress of the foot, with an unsculptured 

 layer of shelly matter; then it lays in a plank (so to speak) between 

 the ventral knob and the "cups," and another on the back extending 

 from the hinge; a ping is securely wedged between this and the beaks 

 of the valves; and, finally, the principal part of the outside of the 

 valves, which is not already protected by the cups, is coated over 

 with large "accessory plates," which, even in their small develop- 

 ment, as shown in the European species, caused Linnaeus to group 

 them with the limpet-like Chitons and the crab-like Barnacles in the 

 heterogeneous order of "inulti valves."" 



These accessory plates so tightly wedge the creature into one par- 

 ticular position that it seems impossible for it even to twist round; 

 and in extricating specimens from the matrix it is hard to avoid 

 breaking the Shell. When a burrow is broken across longitudinally, 

 a stratified gray lining is seen in the part between the siphon pipes 

 and the tangent to the burrow. The same part in Gastrochama is 

 filled with shelly layers; but the Pholad appears to swallow, and, so 

 to speak, digest the abraded matter, as he goes along, giving the 

 matter out again in this altered form. In addition to this singular 

 structure, the burrows, especially of aged individuals, frequently dis- 

 play an irregular chamber communicating with the furthest extremity, 

 the sides of which are' fashioned in very coarse wrinkles, presenting 

 very much the aspect of some of the water-worn chambers of the 

 Mammoth Cave in extreme miniature. Now r in these cavities is fre- 

 quently found the hard, black, horny substance before alluded to, 

 which I take to be the dried foot of the animal, and which is probably 

 strengthened with silicious particles. f 



The only explanation 1 can offer of these curious excavations, 

 which have never before been observed, is, that the foot having lived 

 an active life so long, but being no longer needed for the economy of 

 the animal, does not feel easy in subsiding into a state of complete 

 inactivity, but edges its way through-the very narrow anterior chink 

 (or more likely remains permanently outside it) and employs itself in 

 moving backwards and forwards, thus producing the irregular wrin- 

 kles. Sometimes these "foot-prints" make their way to the inner 

 surface of the Spondylns valve; in which case the oyster lays a coat- 

 ing of shell over it. The foot wears away this, and the oyster lays 



'■• It is very easy, from our advanced point of view, to show the strange errors of the 

 very artificial system of classification which Linnjeus devised for the Mollusks; far more 

 untruthful, though not more artificial, than his arrangement of the plants. It was all, 

 however, that we had a right to expect at that time ; and necessarily resulted from the " col- 

 lector spirit'' which had prevented the shells from being regarded as a part only of a living 

 animal. His arrangement of these animals (apart from the shells) prefigured the classes of 

 Cuvier, which still maintain their place, if not their rank. If we are disposed to find fault, 

 let it not be with the old naturalists, whose works it were, perhaps, better for science some- 

 times to disregard ; but with those who now persist in adhering to the Lamarckian ideas, 

 which are quite as much behind our present knowledge as Linnftus was bt hind his stand- 

 point. The last six years have, perhaps, contributed more to our knowledge of Malacology 

 than the whole of previous researches put together. 



t Any chemist desiring to analyze the gray lining or this black matter will find specimens 

 preserved for that purpose iu the Albany Museum. 



