289 
gelatinous coencecia are spherical, ellipsoidal, or often somewhat 
flattened. The longest diameter of these floating masses often 
exceeds 30 cm. 
Plumatella repens .—This is by far the most abundant bryozoan 
in our locality, being found everywhere on submerged vegetation 
in the backwaters. It often develops with surprising rapidity on 
the submerged stems of plants, where, as in 1896, summer floods 
reinvade the vegetation-covered margins of reservoir backwaters. 
It is represented in the plankton by its floating statoblasts. Their 
seasonal distribution shows some correlations with temperature, 
hydrographic conditions, and the seasonal cycle of the parent 
organisms. During the period of minimum temperatures (Decem- 
ber—February, inclusive) they are relatively rare in the plankton, 
appearing in 30, 8, and 20 per cent., respectively, of the plankton 
catches. They are rare in high- as well as low-water conditions, as, 
for example, in the floods of 1895-96 and 1898, when they appear 
in but one of 15 collections. With the rise of temperature in March 
they occur more frequently, as, for instance, in 1898 (Table I.), and 
continue during the run-off of the spring flood. The occurrences 
rise in March—May to 60, 46, and 50 per cent. of our total collections 
in these months, and the numbers also are larger. For example, in 
1898, 81 per cent. of the total individuals for the year were found 
in these months. The discharge from impounding backwaters, the 
principal breeding grounds of the parent organisms, doubtless tends 
to increase the numbers of statoblasts in channel plankton during 
‘this season. During the remainder of the year, June-November, 
the percentage of occurrences again falls to 30, 50, 24, 32, 18, and 
At per cent., respectively. The 50 per cent. in July is due to the 
summer flood of 1896. If this year is omitted the record falls to 
33 per cent. The large percentage for November is probably due to 
the predominantly higher levels of this month, to the invasion of 
lake margins seeded with statoblasts, and to the increased activity 
in the fishing industry, which tends to disturb the summer’s growth 
of vegetation in tributary backwaters. The relations to the seasonal 
cycle of the species are patent. The summer months, June— 
September, are the season of growth and spread of the parent 
organisms and of the formation of statoblasts, especially as receding 
levels expose the water margins. Hydrographic or other disturb- 
ances tend to increase the number of statoblasts in the plankton 
