248 On the Larval Forms of Spi orbis borealis. { March, 
well as the different habitat of the young and adults, the free- 
swimming larva is often unrecognized or not connected with the 
genus of which it is the young. 
I have often, in former years, captured the larval Spirorbis by 
surface fishing, but up to a short time ago have been unable to 
discover to what adult it belongs. Last summer I was fortunate 
enough to raise these larve from the eggs, and am now able to 
state definitely most of the changes in external form which Spi- 
rorbis goes through between the last stages of the segmentation 
of the egg and the time when it fastens itself to some foreign 
object and begins its sessile and adult life. 
The eggs of Spirorbis borealis are easily obtained in considera- 
ble numbers, If live adults, enclosed in their cases, be placed in 
a proper receptacle in water, and the calcareous shells crushed, 
among the fragments there will be found chains composed ot 
bead-like strings of ova strung along together. These chains are 
easily distinguished from the other soft parts of the Spirorbis 
body by their brown or red color. I found a good way to obtain 
the eggs was to place a number of Spirorbes in a watch crystal 
with water and then crush the cases with a spatula. Remove the 
fragments of shells and the strings of eggs are easily seen at the 
bottom of the watch crystal. 
As the adult Spirorbis is very hardy the young can easily be 
raised from the adult by keeping the latter in an aquarium for a 
few days, when multitudes of the young make their way out of 
the worm cases and can be easily found swimming at or near the 
surface of the water in which they are kept. The young from 
_ which the present studies were made were taken in the months of 
_ July and August, 1884. 
_ The eggs of Spzrorbis borealis have a reddish-brown color and 
are arranged side by side in short strings composed of from one 
to four rows of from ten to fifteen or more eggs each. The later 
stages in the segmentation of the egg resemble those of other 
chetopod eggs and can easily be studied in strings taken from 
the Spirorbis cases. The younger stages of the segmentation 
were not found. Each egg is enclosed in a membranous sac, 
while all the ova lie in a common digitiform structure binding 
them together. The earliest stages in the development of the 
larva are passed through while the eggs are thus enclosed. 
It will be observed that the larvee of Spirorbis now to be de- 
