734 NATURAL HISTORY OF AQUATIC ANIMALS. 



and clearly see the nucleus. The tube or ribbon-secreting organ described by Wright I was unable 

 to discover. 



" When fully extended the basal portion of the animal becomes attenuated to a thin bluish 

 lilaineut, which widens towards the peristome, where the body is over half as thick as the inside 

 diameter of the tube. When fully retracted and resting, the animal resembles in its oblong shape 

 a retracted and resting Stentor, and measures about ^ as long as when fully extended. The 

 ribbon which forms the tube makes from four to twenty-four turns in specimens of different ages." 



This organism I since find to be an inhabitant of the bay also, but is not so abundant as in 

 the creek. Small mica collectors fixed to floating corks in the hatching jars and aquaria used 

 during the past season were found to afford a nidus for Freia as well as Zoothamnium, the latter 

 multiplying at a most astonishing rate in a very few days. Under similar conditions, amoebae, 

 apparently A.proteus, multiplied at a suprising rate; this was the case, too, with a small brown 

 diatom which would coat in three or four days the sides of the glass vessels with a thin brownish 

 film composed of countless myriads of individuals of the one species. The temperature of the 

 bay-water used in the aquaria at this time would range from 76 F. to 89 F. The Vorticellidw 

 also soon attach themselves, and next to the hypotrichous iufusoriaus found in the locality are the 

 most important animalcular forms found in the Chesapeake. At the mouth of the Cherrystone 

 River I last year found Licnophora cohnii in great abundance eutoparasitic upon an unidentified 

 hydroid. The ]\e\iozoi)u,Actinophrys sol, is found in the bay and Saint Jerome's Creek, and I think 

 it capable of swallowing dead or enfeebled Oyster eggs and embryos. 



MUTUAL RELATIONS BETWEEN THE OYSTER AND ITS PREY. Mobius calls an Oyster- 

 bank a Bioccenosis or interdependent community of life. The many species of animals found 

 on the banks and beds are no doubt more or less mutually dependent upon each other for 

 subsistence, but this is perhaps not any more true of Oyster-banks than it is of terrestrial 

 fauna;. There are no doubt vast numbers of floating embryos of Oysters .eaten by other 

 animals growing on the beds which bring their food supply to themselves by means of 

 currents produced by ciliary motion. On the other hand, there are no doubt vast numbers of the 

 minute swimming embryos of these, drawn in and swallowed by the Oyster, which may, indeed, 

 for aught we know, in this way swallow many of its own young, for the current produced by the 

 Oyster by means of the cilia clothing its gills is by no means a feeble one, though it is exceeded 

 in power by the current flowing into and out of the siphons of Mya. In the latter I have frequently, 

 upon opening the animal, found several Copepoda plainly visible to the naked eye swimming 

 about in the water in the inferior mantle cavity, which had evidently been drawn in by the inward 

 current. It is plain in this case that very mild means may become effective as prehensile and 

 destructive agents, so as to bring remotely related types into intimate vital relations. 



Though an animal may be apparently invulnerable on account of the effectiveness of its 

 covering, it cannot emancipate itself from the abiding struggle it has to make to obtain food, no 

 matter how passively it may appear to conduct itself. The Oyster has sucb a character, yet it has 

 been apparent from what has been observed before, that it is entirely dependent for a vigorous 

 existence upon the favorableness of surrounding conditions. The beds and banks in a true sense 

 are interdependent communities, whose vigor may no doubt be impaired by the removal of a single 

 one of its members. Suppose we should take away the algae, diatoms, Oyster-crabs, vibrioi^, 

 bacteria, infusoria, in fact all the minute life; we should greatly impair if not destroy the vitality 

 of the beds. While it is true that many of even the smallest forms may destroy food which 

 should properly be consumed by the Oyster, that were it not for the presence of these same small 

 forms some destructive element might attain such a development as to be more injurious still. 



