564 THE AMERICAN NATURALIST. [Vor. XXXV. 
by the ordinary method employed for laboratory material, and 
as a result the preservation of the tissues was not of the best. 
After photographing the animal from the left or abnormal side, 
three entire metameres from different points along the abnormal 
region were carefully removed by free-hand sectioning, mounted 
in balsam, and studied as whole preparations. The remainder 
of the worm was then imbedded in paraffin and a series of 
transverse sections obtained which enabled one to trace the 
different organs through the entire length of the specimen. 
The abnormality, as seen in Fig. 1, is confined to twenty- 
three median somites. Not only is the diameter of the body 
much greater in this region than it is either anterior or poste- 
rior to it, but the number of parapodia to each segment is also 
increased. An extra pair of appendages is present on the 
forty-first metamere, or first abnormal somite (Fig. 1, so." T), 
of the worm. Immediately anterior to this somite there is evi- 
dence of a cicatrix ; the fortieth metamere, however, is appar- 
ently normal, and the interpolated parts make their appearance 
abruptly and in a fully developed condition. Looking at the 
left side of the animal, as in Fig. 1, three series of parapodia 
are seen. Two of these rows (s. and Zx.) are closely approxi- 
mated and ventral in position ; the third set (s.') is dorsal and 
separated from the other two by a region which, from its longi- 
tudinal furrow and general external appearance, might be taken 
for the true ventral side of the worm. This condition persists 
from the forty-first to the fifty-fourth metamere inclusive 
(fourteen somites), the pseudo-ventral region gradually becom- 
ing smaller and finally disappearing at v. As a natural result 
of its disappearance, the two series of parapodia (s.' and dz.) 
approach each other until at about the seventeenth abnormal 
somite (v.) the appendages s., Zx.', and s.' are close together. 
Parapodia s.' and dx.! of this metamere are much smaller than 
s.; their size is further reduced in the next six metameres, and 
in the twenty-third the last evidence of abnormality is to be 
observed. Externally at least, the somite segments of the 
animal are normal. 
Examination of complete metameres in transverse section 
shows better the relations of the external parts and at the same 
