746 NATURAL HISTORY OF AQUATIC ANIMALS. 



iu the adult, though something of the sort, it is asserted by embryologists, appears to be devel- 

 oped in the larvas. As the Oyster lost its power of locomotion IVom the noa-development of 

 the foot, due doubtless to a gradually acquired sedentary habit which has become permanent. 

 the pedal structures have been almost entirely aborted, leaving nothing excepting the poorly 

 developed pedal muscles described by Dall. There is accordingly little or no evidence of the 

 existence of a pedal or foot ganglion in the Oyster, because there is no need for one, as in other 

 forms; it, too, has disappeared with the structure which required its presence. 



Returning to the consideration of the Oyster-crab, it is well known that.it is much relished 

 by many persons. The animal may be eaten alive, and has a peculiar, agreeable sweetish taste. 

 Recently an enterprising New York party has taken to canning them, the supplies for this purpose 

 being obtained from some of the large oyster-canning establishments. The ecor.omic value of the 

 animal as food, although not great, is sufficiently important to demand a passing notice. 



219. PHYSICAL AND VITAL AGENCIES DESTEUCTIVE TO OYSTERS. 



Most of the observations which follow were made at Saint Jerome's Creek, Maryland, but 

 inasmuch as the physical and vital enemies of Oysters appear to be similar the world over, I have 

 no hesitation in reproducing what I have previously published elsewhere. And of physically 

 injurious agents the black ooze or mud found in the vicinity or on the bottom of many of our 

 most valuable beds and planting grounds is probably the most to be dreaded if it accumulates 

 in too great quantity. 



The origin of the black ooze at the bottom can be traced directly to the sediment held iu 

 (suspension in the water which slowly ebbs and flows in and out of the inclosure, carrying with it 

 in its going and coming a great deal of light organic and inorganic debris, the former part of which 

 is mainly derived from the comminuted fragments of plants growing in the creek. This seemed to 

 be the true history indicated by what was noticed in studying the box-collector. The same opinion 

 is held as to the origin of this mud by both Coste and Fraiche in their works on oyster-culture. 



There is probably no worse enemy of the oyster-culturist than this very mud or sediment. 

 It accumulates on the bottom of the oyster-grounds, where iu course of time it may become dee]) 

 enough to cause, serious trouble. Especially is this true of ponds from which the sea ebbs, and to 

 which it flows through a narrow channel. The Jailing leaves from neighboring trees in autumn 

 also contribute to this pollution, as well as heavy rains which wash deleterious materials into it. 



Adult Oysters which are immersed in part in this mud struggle hard to shut it out from 

 their shells. If one will notice the inside of the shells of Oysters which have grown in a muddy 

 bottom, it will often be seen that there are blister-like cavities around the edges of the valves 

 filled with mud, or a black material of a similar character. There is not the slightest doubt 

 in my mind that in these cases the animal, in order to keep out the intruding mud, has had 

 recourse to the only available means at its command. A great many of the Oysters in the pond 

 are affected in this manner, but it is extremely uncommon to find shells of this kind in opening 

 Oysters coining from a hard bottom. It is easy to understand that such efforts at keeping out 

 the mud from the shell will not only waste the life forces of the animal, but also tend to greatly 

 interfere with its growth. The importance, therefore, of artificial preparation is apparent, where 

 it is desirable to establish ponds for the successful culture of this mollusk. 



Only in one case have I observed that the mud tended to impair the flavor and color of 

 the Oyster. In this instance the animal was thoroughly saturated with the black ooze, the very 

 tissues seeming to be impregnated with the color, the stomach and intestine loaded to engorge- 

 ment with the mud, the animal manifesting every sign of being in a decidedly sickened condition. 



