612 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



7. Monotonic Crustacea -Phmlcton. — As the crustaceans surpass all 

 other classes of the animals of the x)lankton in quantitative develop- 

 ment, so they form monotonic plankton far more often than all other 

 classes. Most commonly this simple crustaeean-phinkton is composed of 

 copep'ods, not infrequently entirely of a single species (6, pp. 758, 843). 

 Next to this I have more frequently found monotonic osiracoda -plank- 

 ton; next schizopoda-planMon. Sometimes also there are in these two 

 orders only numberless individuals of a single species, sometimes of 

 many different species, which compose the monotonic plankton, often 

 almost exclusively, and at other times nuxed with additions of other 

 Crustacea, Sagitta, SaJpa, etc. The other above-mentioned orders of 

 crustaceans, which also- ta-ke a considerable part in the constitution of 

 the plankton, the decapods, amphipods, and phyllopods, I have never 

 found in such quantities that they formed more than half of the mass 

 of tow-stuff. On the contrary, such quantities of crnstace^in-Iarva' of 

 one species (e, g., of Le^jas and other cirripeds) occasionally appear that 

 they predominantly determine the character of theplaiditon. 



8. Monotonic Tanicata-Flanldon. — Next to the monotonic forms of 

 plankton, which are comj)Osed of Crustacea and Gnidaria, tliat of the 

 Tunicata m most numerous. Quite preponderant in quanlity are the 

 ThalUliw or iSalpacea' (Salpa and ^SaJpeUa), and among these, especially 

 the smaller species {Salpa dcynocratica-mucronata, S. runcinata-fusi- 

 formis, and related species). I have often taken such monotonic salpa- 

 planLion in the Mediterranean, in the Atlantic and Indian oceans, and 

 have received the same also through Capt. Kabbe from different parts 

 of the Pacific Ocean. Masses of Doliolum and of Copelata {Appendicu- 

 laria, VexiUaria^ etc.) are also commonly mixed witli this in greater or 

 less quantities. Still these planktonic tunicates, on account of their 

 small size, recede before the Salpa'. I know of no instance where they 

 have by themselves formed a monotonic plankton. But this is the 

 case with the nyctipelagic pyrosoma. The (JlialJengcr and tlie Yettor 

 Fisani in the tropics, on dark nights, met with quantities of monotonic 

 pyrosoma-planlcton in the middle of the Atlantic and Pacific. By day 

 not a single one of these "cones of fire" was to be seen, and as soon 

 as the moon arose they went into the depths (8, pp. 32, 34). 



9. Monotonic Fish-PlauMon. — If, with Ilensen, we limit tlie term 

 plankton to the halohios floating x>assively in the sea, we can desig- 

 nate as "monotonic fish-plankton" only the schools of very young and 

 small fishes, which often ai)pear abundantly in the currents, occasion- 

 ally so compact that very few other pelagic animals can find room 

 between them. If one wishes to extend the term still farther, and wipe 

 out the sharp distinction between planMon and neMoUj all those sea 

 fishes (oceanic as well as neritic) which appear in schools, and which 

 play so significant an oecological role in tlie cycle of matter in the sea 

 {e. g., ScopcUda', Clup>eida\ Leptocephalidfe, Scomberoida') will in general 

 belong here (12, p. 51). 



