THE MICROSCOPE. 263 
They are never extruded from the living animal. When their 
formation is begun, the Polyzoan is approaching its death, and 
it is only after death that the statoblasts become freed from the 
body, the soft structures decaying and melting away, while the 
hardened, chitinous winter eggs float out, to remain quiescent 
during the cold of the season, and to have their contents start 
into activity with the warmth of spring. 
Although the majority of the mature animals are permanently 
sedentary, the embryo as it leaves the statoblast is exceedingly 
lively, and as often happens among other of the lower animals 
it bears no.resemblance to the parent. It is a ciliated creature 
that swims about actively for a time, eventually settling down to 
a quiet life, and developing into what the parent was before it. 
I have several times had the statoblasts give exit to these em- 
bryos in a small aquarium standing in a warm room during the 
winter, and they have finally attached themselves to the glass, 
where they seemed to the naked eye like transparent grains of 
rice; when carefully detached for the microscope, their appear- 
ance is always indescribably exquisite. Several of my friends 
have had a similar experience. In every case the statoblasts 
had been gathered accidentally with other materials, and left 
standing in the aquarium, where they probably mistook the 
warmth of the room for that of early spring. 
The winter eggs of each Polyzoan genus are characteristic, and 
from the appearance of even a single one, if mature, its generic 
origin may be ascertained. It is to assist the microscopist in 
that determination that this paper is prepared. It is always a 
satisfaction to know a thing when it is seen, and to be able to 
give a positive answer to the oft-repeated question, ““ What is it?” 
And these little brown specks are sooner or later sure to bring out 
that question. By means of the subjoined Key and the figures 
of the statoblasts in the text, the origin of these aS eggs may 
be determined. 
KEY TO THE STATOBLASTS OF THE FRESH-WATER POLYZOA. 
A Reproduction probably by the urn-shaped segments 
of the stem, , Urnatella. 
Reproduction ne siatoblasts Cai. 
Statoblasts without spines (b). 
Statoblasts with spinous margins (d). 
Without a cellular annulus, . . . . Fredericella, Fig. 1, 
of oP 
