614 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
become adapted to the meteorological conditions, the time of year and 
other conditions 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 influence of meteorological vari- 
ations on the one side, of cecological relations on the other, are of the 
greatest importance for the periodical appearance. Most organisms 
appear 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 remarkable variations” in the plankton composition (9, 
pp. 29, 59); he explains it in part by “ periods of famine” (p. 53). 
Yearly oscillations—The plankton 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 high merit, extending over a series of years, namely 
those of Schmidtleim from Naples (19) and of Graeffe from Trieste 
(20). Even the first glance at the tables, those of the former relating 
to the appearance 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 Schmidtiein 
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 und 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. 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 Cotylorhiza tuberculata, 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). Justas variable is the occurrence—“ according to the 
year”—of Umbrosa lobata and other meduse. Of the six species of ~ 
ctenophores of the Gulf of Trieste, only one appears every year, the five 
others only now and then. Not only do the quantities of individuals, 
but also the “ time of appearance of pelagic animals change according to 
the meteorological conditions of the time of year” (20, v, p. 361). I 
myself can fully establish this proposition 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 
same place on the Mediterranean coast (e. g., in Portofino, in Villa- 
franca), numerously in the first year, rarely in the second, and not at 
all in the third. When,in April, 1873, I fished in the Gulf of Smyrna, 
it was full of swarms of the great pelagic 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 
