24 



THE OYSTER CKAB AS MESSMATE AXl) PrKVEYOR. 



It is many years since Mr. Say named the little oyster- 

 crab of our coasts PinaotJieres ostreuuu and its halnts in 

 relation to tlie oyster seem to have excited but little in- 

 terest, especially in foreign writers. Prof. Verrill. in 

 his report to the U. S. Fish Commission, observes that it 

 is the female which lives in the oyster, and that the male 

 which is smaller and quite unlike the female, is rarely, 

 if ever seen to occur, but that it has been seen by him 

 swimming at the surface of the water in the middle of 

 Vineyard Sound. His statement that it occurs wherever 

 oysters occur. I cannot agree with, since out of many 

 hundreds of St. Jerome's oysters which I saAv opened, I 

 never saw a specimen of PinnotJieres : they may occur, 

 but rarely. This little crab has quite a number of allies 

 which inhabit various living mollusks. holothurians. etc., 

 of which admirable accounts are given by Van Beneden 

 in his work on Animal Parasites and ^1 ess mates. 



There can be no doubt that the oyster-crab is a true 

 messmate, and it is highly probable that the presence of 

 these animals in the oyster is rather to be reo-arded as 

 advantageous than otherwise. The animal lives in the 

 gill cavity of the oyster, and, as will be seen from the 

 followino- observations, may be the means of indirectly 

 sux:)plying its host with a part of its food. During a 

 reconnoitering trip doAvn the Chesapeake on the yacht 

 "Lookout," in the first week of July last, in dredging, 

 some oysters were hauled up which contained Pinnothe- 

 res. In the case which I am about to describe, the inclu- 

 ded crab was a female with the curiously expanded 

 abdomen folded forAvards under the thorax and partially 

 covering a huge mass of brownish eggs. Upon examin- 

 ing these eggs what was my astonishment to find that 

 they afforded attachment to a great number of compound 

 colonies of the singular bell animalcule. ZoUlutmnium 

 arhvsculiLm. Tpon further examination it was found 

 that the legs and back of the animal also afforded jDoints 



