[7 J AN INDIRECT SOURCE OF THE FOOD OF FISHES. 761 



ish cuticle; but for uainbers these were again very greatly exceeded by 

 tlie compound stalked genera of bell-animalcules. Upon the very com- 

 mon alga, Laminar ia, these were abundant, and upon the fronds of 

 another alga, the Grinnellia, in three or four fathoms of water, near the 

 middle of the Chesapeake, their number was truly astounding. In a 

 few such places where these algse were dredged up from the bottom, 

 covered with innumerable colonies of protozoans, it would doubtless be 

 much within bounds to state that there were 1,000 individual i^rotozoan 

 zooids to the superficial square inch of frond surface. At this rate 

 there would be 30,204,000 zooids found to populate a single square rod 

 of frond surface. Estimating the number at only 100 per square inch, 

 which is low, and which would, I think, represent a fair average over 

 considerable areas where the conditions of life were favorable, there 

 would still be a stalked protozoan population of uearly four millions to 

 the square rod. The most abundant of these compound forms was one 

 which very much resembles Zoothamnium alternansj OlaperMe, found on 

 the west coast of Norway. The same form was again found in vast 

 abundance upon algoe in Cherrystone Eiver, near the mouth of the 

 Chesapeake, during the season of 1881. Upon one occasion I found it 

 in great abundance growing on the parts of the body of a Pinnotheres 

 which was living in the gill cavity of an oyster, its swarmers, or young, 

 as they were thrown oft', in all probability forming part of the food sup- 

 ply of the mollusk. 



I have been interested upon several occasions to observe that the very 

 minute stalked, collared monads, Salpingaxa and Codosiga, are frequently 

 to be found attached to the stems of the compound colonies of bell-ani- 

 malcules, or gathered about in the vicinity of the point of attachment 

 of a single one. In such cases the monads appear to derive a benefit 

 from the currents or vortices set uj) in the water by the waving of the 

 ciliary crowns of their giant neighbors, which bring particles of food to 

 their very doors as it were. On one occasion I found individuals of a 

 species of Vorticella fixed to the egg-membrane of the ova of the cod 

 fish at Wood's Holl, Massachusetts, as had been previously observed 

 by E. E. Earll, and in their vicinity were several colonies of a compound 

 stalked monad, resembling the IHnohryon of Ehrenberg. On another 

 occasion I found something like Poteriodendron on the Zoothamnium 

 which covered a Pinnotheres inhabiting an oyster; but the chain ofi^ar- 

 asitism did not stop here, for on the monad as well as on the bell-animal 

 there were rod-like bodies attached which were presumably bacteroid, 

 as has been supposed by Stein. Stalked monads are probably much 

 more common than has been supposed, which reminds me that I have 

 detected the occurrence of Rhipidodendron splendidum in the bogs and 

 ponds of New Jersey, a form which was described originally by Stein 

 from Bohemia. Minute as the stalked monads are, they must live on 

 still minuter beings, probably upon Microbia, or Sehizomycetcs, a group 

 of fungi, now known to be the active agents in i>utrefactive changes 



