110 BULLETIN OF THE BUREAU OF FISHERIES 



smaller copepods form a considerable item in the diet of Temora. Calanus, however, 

 she found chiefly vegetarian, and Pseudocalanus perhaps exclusively so. Marshall's 

 (1924) more recent study of the gut contents of large numbers of Calanus taken 

 throughout the year in the English Channel corroborates this, diatoms proving the 

 chief article of diet in spring and autumn with peridinians (curiously enough, however, 

 no Ceratium) in summer. Silicoflagellates were also eaten in small quantities, 

 while a few of the Calanus had eaten other copepods, molluscan larvse, and tintinnids. 



All the Tomopteris I have examined have been empty, which has been the 

 experience of most students, but it is probable that they are vegetable feeders chiefly, 

 Lebour (1922 and 1923) having found diatoms their principal diet, with some green 

 flagellates. Tomopteris, however, sometimes turns carnivorous, for she watched 

 one swallow a Sagitta whole and saw another that contained a larval herring. All 

 the shell-bearing pteropods (Limacina retroversa, for example) are also vegetarian, 

 dieting chiefly on diatoms. The Salpse likewise feed on diatoms, peridinians, and other 

 small organisms, animal as well as plant, their gut contents and foecal masses having 

 long been a treasure house to the student of the microscopic plankton. For example, 

 the "guts" of large S. tilesii collected south of Nantucket Lightship in July, 1913 

 (station 10061), contained a varied assortment of diatoms, Peridinium, and Ceratium, 

 besides an occasional newly-hatched Euthemisto; but the most successful captors 

 of the unicellular pelagic plants are the appendicularians, which, thanks to their 

 very fine-meshed straining apparatus, are able to utilize gymnodinids, rhizopods, 

 naked flagellates, coccolithophids, 52 etc., forms so tiny that for the most part they 

 pass through the finest tow nets. Appendicularians likewise devour the larger 

 protozoans and unicellular plants. For example, a large Oikopleura vanhqff'eni from 

 the neighborhood of Lurcher Shoal (May 10, 1915, station 10272) was packed with 

 the horns and other fragments of Ceratium, besides small Peridinium of several 

 species, tintinnids, and silicoflagellates (Distephanus). 



None of the pelagic tunicates are plentiful enough in the Gulf of Maine to make 

 serious inroads on the phytoplankton. In the Gulf Stream to the south Salpte 

 sometimes occur in hordes, and on such occasions strain the water bare (Bigelow, 

 1909). 



Among the unicellular planktonic animals the infusorians are proverbially rapa- 

 cious. The tintinnid genus Cyttarocylis has been found to contain a great variety 

 of microsocopic organisms — e. g., Peridinium, Dinophysis, Goniaulax, and diatoms 

 (Lebour, 1922) — and even the Infusoria, which are provided with chromatophores, 

 are known to take solid food (Steuer, 1910, p. 627). Radiolarians engidf diatoms, 

 tintinnids, and other Infusoria; hence, when Acanthometron swarms in the gulf 

 (p. 460) it must locally take heavy toll of other microscopic animals and of planktonic 

 plants. Foraminifera are also rapacious animals, but have never been found plentiful 

 enough in the plankton of the Gulf of Maine to be of any great importance in the 

 economy of its planktonic communities. 



On the border line between plant and animal, so far as their mode of nourishment 

 is concerned, stand the peridinians, for while the shelled forms are typical producers 



"For an account of the food of appendicularians see Lohmann (1903, p. 23, pi. 4) and Johnstone (1908, p. 139). 



