614 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



become adai)te(l to the meteorological coiKlitions, the time of year and 

 otlier conditions of life in tlie " struggle for existence, " so also tlie 

 annual development of most marine aninmls is governed by definite, 

 inherited habits. With them also the intiuence of meteorological vari- 

 ations on the one side, of oscological relations on the other, are of the 

 greatest importance for the periodical appearance. Most organisms 

 aijpear in the plankton only periodically, and only very few can be 

 reckoned as belonging to the " perennial plankton" in Hensen's sense 

 (9, p. 1). This investigator also attaches great importance to the tem- 

 poral "highly remarkal)le variations'' in the plankton composition (9, 

 pp. 29, 59); he explains it in part by " periods of famine" (p. 53). 



Yearly oscillations. — The i)lankton literature has hitherto contained 

 only a few reliable statements upon the yearly variations, which underlie 

 the appearance of the pelagic animals and plants. Still there are a few 

 contributions of liigh merit, extending over a series of years, namely 

 those of Schmidtlein irom Naples (19) and of Graeffe from Trieste 

 (20), Even the first glance at the tables, those of the former relating 

 to the ai)pearance of the i^elagic animals in the Gulf of ISrai)les, shows 

 us how remarkably different was the action of the majority of these 

 in several successive years. As there are good and bad wine and fruit 

 years, so there are rich and barren plankton years. But Schmidtlein 

 correctly remarks that extensi\e observations extending through a 

 long series of years are demanded to gain a deeper insight into the 

 meaning of these yearly and monthly variations shown in the tables. 

 The same view is also held by Chun, Avho, in his monograph of the 

 ctenophores of the Gulf of Naples (p. 236), points out how very differ- 

 ent was the number of these in five successive years. 



Graeffe, resting on the basis of his observations for many years, says 

 of CotylorMza tuberenlata, that this beautiful acaleph has not for many 

 years been found in the Adriatic, in other years only individually, but 

 not at all rarely (yet always only in the three months of July, August, 

 and September). Just as variable is the occurrence — ^^ according to the 

 year'''' — of Umhrosa lohafa and other medusa^ Of the six species of 

 ctenophores of the Gulf of Trieste, only one a^ipears every year, the five 

 others only noAv_ and then. Not only do the qnantities of individuals, 

 but also the " time of appearance of pelagic animals change according to 

 the meteorological conditions of tlie time of year" (20, v, p, 361). I 

 myself can fully establish this proposition on the ground of observa- 

 tions which 1 have made in the course of many years of medusa 

 studies. Many of these "capricious beauties" occur in one and the 

 same place on the Mediterranean coast {e. g., in Portofino, in Viila- 

 franca), numerously in the first year, rarely in the second, and not at 

 all in the third. When, in April, 1873, 1 fished in the Gulf of Smyrna, 

 it was full of swarms of the great i)elagic Chrysaora hyoscella. In 

 April, 1887, when for the second time I sought the same gulf, I could 

 not find a single individual of that beautiful medusa, but instead the 



