OUR FRESH-WATER POLYZOA. 
309 
The young animal makes its appearance in the spring of the 
year as a single Polypide, which, however, cpiickly produces 
others, until the colony attains the size of one or two inches by 
July and August, at which time there may be found an im- 
mense profusion of statoblasts in most of the genera. 
The Fresh-water Polyzoa may be kept alive in a vessel of 
water for two or three months if care be taken to supply them 
with abundance of food (for they are voracious feeders), and 
to keep them well shaded from the light, for all the species, 
except Gristatella, love dark habitations. I have found Frede- 
ricella the most long-lived in an aquarium. As an instance 
of the capacity of a Polyzoon’s appetite, I may record that 
a few years ago my aquarium was almost as green as pea-soup 
from the abundance of algae spores ; I put a good sized 
specimen of Alcyonella fungosct into the water, and in about an 
hour’s time it was quite clear. 
Most of the Fresh- water Polyzoa prefer clear lakes and mill- 
pools, but Alcyonella is by no means so particular, being 
found in water where there is much mud ; Alcyonella fungosa 
assumes a spongoid form and grows to a very large size ; the 
interstices of the caengecium harbour a multitude of all sorts of 
aquatic animals, Annelids, Crustacea, and the larva? of various 
insects, &c., &c. It is advisable to pay attention to these hosts 
of Alcyonella, as some few years ago I was rewarded by the 
discovery of a very rare worm, whose occurrence in this country 
rested on doubtful evidence ; this was the Fingered ISTais ( Proto 
digitata), which protruded the curious digitiform segments of its 
tail out of the mass of Alcyonella fungosa .* 
The Fresh- water Polyzoa have not been studied in this 
country at all as they deserve ; it is true that we have Allman’s 
admirable monograph of this group, in which work all known 
species are described and figured ; but it is probable that 
careful searches may reward the collector with the discovery 
of new species, while his observations may tend to throw 
light on some points of their economy which require eluci- 
dation. 
Professor Allman enumerates sixteen British species, and 
believes the number of known species to amount to twenty-one. 
It is curious to notice that until within the last few years not 
a single species of Fresh-water Polyzoa had been discovered 
south of the Mediterranean in the Old World, or of Philadelphia 
in the New. In 1860, however, Mr. 0. D’Oyly H. Aplin found 
several specimens of this family, comprising at least two species, 
in Australia. One specimen he described t as having elongated 
* See “ Annals and Magazine of Natural History,” Dec., 1860, p. 393. 
t Ibid, p. 454. 
