148 A CATERER TO MINE OYSTER. 



not seem to trouble the natural growth. Tolled by broken oysters, when 

 the planter is working, they assemble in crowds. One man told me that 

 he had had five hundred bushels of seed destroyed by these crabs with- 

 in a week. While he was planting he conld see the pests, and thought 

 they numbered one to every fifty oysters. A similar report comes from 

 the Chesapeake Bay region. It is well known that in Europe crabs are 

 very destructive to the planted beds, and it is quite possible that many 

 mysterious losses may be charged to these rapacious and insidious robbers. 

 Aldrovandns, and others among the naturalists of the Middle Ages, 

 entertained a singular notion relative to the crab and the oyster. They 

 asserted that the sly crab, in order to obtain the flesh of the oyster, with- 

 out danger to its own claws, watched its opportunity when the shell was 

 open to advance without noise and cast a pebble between the valves, 

 preventing their closing, and then extracted the animal in safety. "What 

 craft," exclaims the credulous author, " in animals that are destitute of 

 reason and voice !"* 



* In respect to the little crab which becomes red in the cooked oyster, but is greenish- 

 brown in life, opinion is divided as to whether its presence is of any harm to the oyster 

 whose shells give it shelter, but the probability is that it is not. Its scientific name is 

 Pinnotheres ostreum, and it seems to be a parasite. It slips in and out of the oyster al- 

 most at pleasure, and enjoys a portion of all the good things the oyster feeds upon. We 

 are told that it is the female alone which dwells in the oyster, and that males are almost 

 never seen by the most careful searchers. Several allies inhabit various living mollusks, 

 holothurians, etc. In the report of the Maryland Fish Commission for 1881, Professor 

 J. A. Ryder gave some interesting particulars in respect to this little crab, which, from 

 its nook in the oyster's gill- cavity, may be the means of indirectly supplying its host with 

 a part of its food. Professor Ryder found attached to the crab a great number of com- 

 pound colonies of the singular bell animalcule, Zoothamnium arbusculum, and that here 

 and there numerous minute rod-like vibriones had affixed themselves by one end. "In 

 this way it happens that there is a quadruple commensalism established, since we have 

 the vibriones fixed and probably nourished from the stalks of the zoothamnium, while 

 the latter is benefited by the stream of water drawn in by the cilia of the oyster, and the 

 last feeds itself and its protege, the crab, from the same food-bearing current. Possibly 

 the crab inside the shell catches and swallows food which in its entire state could not be 

 taken by the oyster ; but in any event the small crumbs which would fall from the mouth 

 and claws of the crab would be carried to the mouth of the oyster, so that nothing is 

 wasted. "We must consider the crab, with its forest of bell animalcules, in still another 

 light. Since the animalcules are well fed in their strange position, it is but natural to 

 suppose that they would propagate rapidly. They multiply in two ways, viz., by divid- 

 ing both lengthwise and crosswise, one -half of the product being set free, and known 

 swarmers. These cast-off germs of the animalcule colonies are no doubt hurried along in 

 vortex created by the cilia of the gills and palps, carried to the mouth, and swallowed as 

 part of the daily allowance of the food of the oyster. We are accordingly obliged to look 

 upon the pinnotheres in this case as a veritable nursery, upon whose body animalcules 

 are continually propagated and set free as part of the food-supply of the oyster, acting as 

 host to the crab." 



