146 BRODE. [VoL. XIV. 
At all seasons of the year excepting two weeks in July the 
worms multiply by fission. This takes place slowly in the 
winter and very rapidly during the summer. The new head 
and tail form almost completely in the region of fission before 
separation takes place. In the summer fission occurs as often 
as three times a week. In a dish in which one worm was 
placed, eight were found at the end of one week. At the end 
of two weeks fifty were counted. 
The fission zone is formed near the middle of a segment and 
not between two segments, as has been described for some 
other Naidomorpha. In so far as I have observed, the regen- 
eration of head and tail in cases of fission occurs in the one 
somite in which the fission zone first appears. The number of 
segments formed in the new head is constant, being five, while 
the number in the new tail varies, — in fact there is no limit to 
the growth of the tail. Usually twelve to sixteen segments are 
visible before second fission occurs. When fission occurs in an 
anterior individual the zone appears in the first new segment of 
the previous fission zone. 
Three fission zones may be present in one worm during the 
period of rapid multiplication. More than three have not been 
observed by me. 
At the first outward signs of fission the worm has from 
thirty to forty segments and measures from 5 to 6 mm. in 
length. When the worms are ready to separate there are from 
fifty to sixty segments, and the length has increased to 10-11 
mm. The number of the segment in which fission occurs is 
fairly constant, but is liable to vary. In all observed cases it 
occurs back of segment XVII and usually anterior to segment 
XXII. 
If a worm is divided by cutting, both parts will continue to 
live and in a short time will regenerate a new head and tail 
and form perfect individuals. There seems to be some limit, 
however, to the number of segments which will regenerate a 
new head or tail. 
My experiments have not been extensive enough to establish 
any rule regarding regeneration, but they have shown that the 
number of segments regenerated at the anterior end of the 
