Juday—Lakes in Central America. 
239 
The cladoeera consisted of Daphnia tongispina var. Tiyalina 
and Ceriodaphnia pulchella. A very few specimens of the 
former were found below 50 m. The latter was fairly abundant 
in the upper 25 m. 
The general results that have been obtained by marine plank- 
tologists show that plankton organisms are present in much 
smaller numbers in the tropical parts of the sea than in the tem¬ 
perate latitudes, or even within the polar circles. To cite but a 
single instance, Lohmann 1 found a much larger number of organ¬ 
isms north of 30° north latitude and south of 25° south latitude 
in the Atlantic ocean than between these two parallels. In the 
main the greater number in the higher latitudes was due to a 
greater variety of forms, the most conspicuous increase being 
due to diatoms. But the Coccolithophoridae and the Peridinidae, 
which were the common forms from the English Channel to 
Buenos Ayres, also reached their maximum numbers beyond the 
parallels mentioned above. 
Table III (p. 246) shows that there was no marked paucity of 
net plankton in these four tropical lakes at the time of these ob¬ 
servations. In fact the material compares very favorably in 
quantity with that of lakes situated in temperate latitudes. The 
shallowest member of these tropical lakes, Amatitlan, possessed 
the greatest variety of forms. With the exception of its rotifer 
population the abundance and variety of forms were quite as 
great as might be expected from temperate lakes of similar size 
and depth. 
A few months after the observations were made on these tropi¬ 
cal lakes i. e., in August, 1910, similar observations were made 
on several of the Finger Lakes in the state of New York. In 
both instances, the catches were made with the same net and the 
material was preserved and counted in the same manner. The 
results obtained with the vertical closing net on the shallower 
of the Finger Lakes have already been published, but those ob¬ 
tained in the same manner in Cayuga and Seneca lakes, the 
deeper of the Finger Lakes, have not been published hitherto and 
are included here in the latter part of table III (p. 246) for the 
purpose of comparing these catches with those obtained on the 
deeper tropical lakes. 
A comparison of the cladoceran population of lakes Atitlan 
1 Veroeffentlieh. d. Instituts f. Meeresk., Univ. Berlin, N. F., Geogr. Natur- 
wiss. Reihe, Heft 1, 1912. 92 p., 2 pi. 
