SOURCES OF MARINE FOOD. 
355 
food of the scup, however, is somewhat more varied, comprising a wider range of 
victims, but of the same general character as belong to the bottom fauna. Thus 
one finds, in fish taken by hook and line, a great quantity of amphipods, some of the 
compound ascidians ( Leptoclinum ), many small lamellibranch mollusks, and at times 
very many of the sand-dollars ( Echinarachnius parma) ground up with sand and 
deep black mud of the bottom from which they were feeding, just above which also 
the amphipods are usually so abundant. 
Now, on the floor of these littoral waters the food of the lamellibranch mollusca is 
of course drawn from the microscopic organisms living suspended in the water above, 
which the animal obtains from the currents of water passing through its gills and 
mantle. The tautog, therefore, which consumes these molluscan victims to so large 
an extent, is only one step removed from their primary food supply of microscopic 
organisms, and is directly dependent upon such a supply, although not quite actually 
using it itself. So also the predaceous gastropods which feed upon other mollusks 
are directly conditioned upon the ability of some members of their food supply, by 
however many steps in the series they may be removed, to obtain the microscopic 
organisms from the surrounding water. 
With regard to the great group of the Crustacea I have not yet had the oppor- 
tunity of demonstrating the steps by which their victims are passed on from one form 
to another, from the primary feeders upon microscopic food up to the higher forms. 
They are fierce devourers of their own kindred at least, as maybe abundantly proven 
if any one group — as the crabs — be investigated, for smaller species are constantly 
preyed upon by the larger. They are scavengers to some extent, as dead material 
comes to them, and they also secure the young fish alive when their size will permit 
them, but the necessity of masticating their food before eating makes the identification 
of the material harder to follow. 
It is entirely probable that some vegetal feeders may be found among the adult 
Crustacea, as is certainly true to some extent in Panopeus , but the larval history is 
without doubt largely conditioned upon the Protozoa and Protophyta, amid which the 
earliest free-swimming stages are passed. Vegetal feeders, indeed — i. e., those using 
marine algrn and the like— may exist in every large order of animals, but under the 
present conditions they are manifestly quite too few to supply the food material of the 
larger carnivorous forms, and we are inevitably brought back to a food supply similar 
to that of the menhaden, which forms the stable basis upon which marine animal 
organisms of all classes are laid. This is not a new fact, of course, but it is one which 
will bear demonstrating in many ways and under many circumstances. Professor 
Brooks has recently shown * how all marine life has been evolved out of these ancient 
pelagic conditions; and any rational and thorough consideration of fisheries problems 
must eventually descend in steady steps to them. 
There have now been shown in several cases how marine food is elaborated, as it 
were, along different lines, from the primary sources of supply; the squeteague and 
bluefisli stand farthest removed in one way, the sea bass in another, the scup and 
tautog less distantly in another. Many fish, such as the herring, alewife, and shad, 
fall into another group, since they use mainly the minute Crustacea; and so the plan 
might be enlarged to include many other species, always leading back, however, to 
the microscopic basis which is so easily demonstrated through the feeding processes 
of the mussels and the menhaden. 
* The genus Salpa, p. 167. 
