614 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



become adiiptod to tlie iiieteoiolooical conditions, the time of year and 

 other coiiditious of life in the " struggle for existence, " so also the 

 annual development of most marine animals is governed by definite, 

 inherited habits. "With them also the intluenc<* of meteorological vari- 

 ations on the one side, of (ecological relations on the other, are of the 

 greatest importance for the periodical ai)pearance. Most organisms 

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

 reckoned as belonging to the '' i)erennial plankton'' in Hensen's sense 

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

 j)or(d "highly remarkable variations" in the plankton composition (9, 

 pp. Ii9, 50); lie explains it in i)art by " periods of famine" (p. 53). 



Yearly oscillations. — The plankton literature has hitherto contained 

 only a few reliable statements ui)on the yearly variations, wiiich underlie 

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

 contribntions of high merit, extending over a series of years, namely 

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

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

 to the a])i)earance of the pelagic animals in the Gulf of Naples, 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 extensive 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, who, in his monograph of the 

 ctenophores of the Gulf of Naples (p. 230), points out how very differ- 

 ent was the number of these in five successive years. 



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

 of Cotylorhiza ttiherculata, that this beautiful acaleph has not for many 

 years been fouiul 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 lohata and other medusa\ Of the six species of 

 ctenophores of the Gulf of Trieste, only one appears everj'^ y<?iii", the five 

 others only noM' and then. Not only do the quantities ofindividnals, 

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

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

 myself can fully establish this ])roposition on the ground of observa- 

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

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

 sanu^ place on the Mediterranean coast {e. </., in l*ortonno, in Villa- 

 franca), nunu;rously 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 Smyina, 

 it was full of swarms of the great ])elagic Chrysaora hyoscclla. In 

 Aj)ril, 1.SS7, when for the second time 1 sought the same gulf, 1 could 

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



