122 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



history being measured almost by moments — is such as to insure a stable basis of 

 existence to those species depending upon them. Indeed, it is little wonder that 

 these fish are so fat when their food supply is considered. 



Another important consideration in the make-up of the menhaden food is its vegetal 

 character to so great a degree. The predominance of the many species of diatoms 

 a,ud Peridinium; the swarm spores, oscillatoria, and fungous threads contribute directly 

 to the food of the animal itself, and indirectly through the large infusoria and cope- 

 pods. Of the large family of infusoria — Tintinnodea — so abundant in the foregoing 

 descriptions of the menhaden food, Daday says : * 



' Iui Haushalte der Natur spielen sie (lurch ihre Gefrassigkeit eine ziemlick bedeutende- Rolle, 

 indem sie ausser den kleinen Diatomeen, Algen und anderen Piianzenresteu aucli viele verfaulte 

 organiscke Stoffe versckliugen. 



He also goes on to say that they do not shun microscopic animals, but repeatedly 

 can be found having eaten Dinojlagellates, Peridinium and Dinophysis; even their own 

 relatives — Codonella, Tintinnopsis, etc. This is also no doubt true of many of the 

 other infusoria gathered by the menhaden. In the iigures of the infusoria of the 

 Gulf of Naples t Entz represents very many of these organisms with diatoms within 

 their cytopasm. The copepods, which are the most important animal constituent of 

 the food material, feed, I am very sure very largely upon the same vegetal diet in these 

 localities here considered as is taken by the menhaden. The alimentary tract of the 

 copepods is filled with a greenish-yellow colored mass of material, in which one may 

 often identify the small vegetal cell so abundant in tig. 6 (plate 2), which by reason of 

 its minuteness has escaped the crushing up in the process of feeding by the animal. 

 In an arm of Childs River, Waquoit Bay, it is almost certain that the abundant cope- 

 pods of the surface water were filled with the small Rajjhidium polymorplmm, which, 

 together with very many other forms of oscillatoria, made a large part of the material 

 gathered by the fish, which organism was so abundant in the stomach of the menhaden. 

 Another important place in the elaboration of this vegetal microorganic food supply 

 is undoubtedly filled by the bacteria, whose abundance and even presence are so 

 unsuspected in the ordinary study of microorganisms of surface waters. Dr. H. L. 

 Russell, speaking of the diminution of land bacteria as one leaves the shore and pro- 

 ceeds into dense sea water, says : % 



Die gewobnlicken Spaltpilze, welclie im siissen Wasser und im Erdboden vorkanden sind, werden 

 durck die Tkatigkeit des Seewassers und der darin enthaltenen Mikroorganismen zerstort. 



Dr. W. T. Sedjwick tells me that in his opinion the bacteria are freely used as 

 food by the larger infusoria. The many bacteria in the so called amorphous matter 

 and those brought by fresh- water streams into brackish water do doubtless contribute 

 no small element to the food supply of the infusorial organisms there swarming. 

 Vegetal diet upon the unicellular plants is, therefore, very plainly to a great extent at 

 the basis of the menhaden food;§ while the fish subsist very largely upon those organ- 

 isms directly, gathered by their pharyngeal filters, and indirectly upon the same 



* Monograpkie der Familie der Tintinnodeen, p. 512. 



t Ueber Infusorien des Golfes von Neapel, pi. 20-22. Mitt, aus der Zool. Station zu Neapel, Bd. 5. 



tUntersuckungen iiber im Golf V. Neapel lebeude Bacterian. Zeitschrift fur Hygiene und Infec- 

 tionskrankheiten, Bd. 11, 1891, pp. 167, 213. 



$ See also Ryder, U. S. F. C. Bull. 1878, p. 242. Tbe Protozoa and Protopkytes considered as tbe 

 primary or indirect source of tke food of iiskes. 



