ON THE FOOD OF THE MENHADEN. 117 



noticed young annelids in fish taken in the seine by daytime, while the Crustacea are 

 also less abundant; especially noticeable is the lack of schizopod shrimps, the fewer 

 copepods. But by far the most constant features of the menhaden food in this district 

 are the unicellular elements in it, especially the unicellular plants, and of these the 

 various genera of the family Peridinium easily predominate. 



In plate 3, fig. 7, is represented a camera drawing of one field of the microscope, 

 under a magnification of 178 diameters, of the organisms as they appear in the mate- 

 rial collected from the surface waters of this estuary by means of the sand filter just 

 described. The great majority of the organisms are Glenodinium, some of the most 

 characteristic of which are shown &tp, fig. 7, in the various positions of the cells. A 

 good description of the characteristics of the marine Peridinium and the life-history 

 has been given by George Klebs,* and it is easy to make out the general plan of their 

 structure in this material. There are also taken at the surface here other pear-shaped 

 alga swarm-spores r, besides many diatoms, of which, however, only a few are here 

 shown. The Infusoria are an important factor in this surface material; some are the 

 small green (t) which are very numerous; most abundant, however, are the small 

 bean- shaped fiagellates (s), which go winding their way in among the other material 

 upon the slide when all else, is motionless. All these organisms finally are mixed 

 together in a greater or less quantity of amorphous matter — flocculent bunches of 

 greenish and yellowish color, just such as are to be found in filtering any surface 

 waters. Dr. W. T. Sedgwick tells me that in his opinion the color of this is due to 

 the presence of bacteria masses of the Zobglea form. There is also no doubt the 

 detritus from disintegrating organic material of many kinds. All this matter is highly 

 phosphorescent when concentrated upon the sand in the tube of the funnel in the 

 course ot filtration, as may be seen by disturbing it in the darkness. 



Compare now with fig. 7, fig. 8, which represents in a similar manner one field of 

 the microscope drawn with camera, exhibiting the same organisms taken from the 

 stomach of a menhaden; the fish was feeding in the locality just mentioned where the 

 surface waters were filtered. The same Peridinium is present and in the same large 

 proportion to the other forms of living material, except that the smallest organisms — 

 infusoria, etc., of fig. 7 — do not appear in this material to any great extent. This may 

 be due to the fact that the very smallest actively moving organisms may pass through 

 the meshes of the pharyngeal filter, which may be readily conceived on account of 

 their minute size, or they may be so mixed up in the mucous and amorphous matter in 

 the fish's stomach as to escape detection to a great extent. It is easy to see the 

 complete identity between living organisms filtered from water by mechanical contriv- 

 ance and those secured by the menhaden feeding in the same waters by means of his 

 anatomical specialization, giving a demonstration that the menhaden is a surface 

 feeder — taking the organisms suspended in the water in a very complete manner. 



It must not be imagined from the foregoing figures that the waters there contain 

 no other organisms than Peridinium; the percentage of diatoms is very great, not to 

 mention the annelids, rotifers, and Crustacea, before enumerated, which latter were 

 (except the Crustacea) found only in this locality in the stomach contents of the fish. 

 In fig. 16, pi. 7, are represented some of the more important diatoms selected from 

 the food taken from several fish in this locality ; there is also an occasional alga thread, 



f In the Botaaische Zeituug, Nos. 12 and 14, 1884. 



