148 BRODE. [VoL. XIV. 
Methylen Blue. — A solution of the stain was made by dis- 
solving a small amount of the powder in water; a very small 
drop of this was added to a drop of clear water on the slide in 
which was a live worm. A cover glass supported on wax feet 
was placed over this and the examination was made with the 
compound microscope. Within two hours the peripheral nerv- 
ous system would be well stained. Specimens were also 
killed by adding a drop of 2% formalin to the slide on which 
they were placed. The methylen-blue solution was then 
added. This gave the best results in the study of the sense 
organs, while the peripheral nerves took the stain only when 
the specimen was alive. 
Imbedding. — Specimens were imbedded in paraffin and were 
cut from 5 » to 15 pw thick. 
Drawing. — Drawings were made by aid of the Zeiss-Abbé 
camera lucida, and a number of points were worked out by 
means of reconstructions and composite drawings from camera 
sketches. The majority of the figures were drawn at a 
magnification of 400 diameters, and all were reduced one-half 
in reproduction. 
III. MORPHOLOGY. 
1. THE Bopy WALL AND EXTERNAL CHARACTERS. 
(a) Segmentation. 
The number of segments in an individual depends upon its 
condition. If sexually mature it may have from twenty-five to 
thirty-five. This period is so short that the growth in length 
in the tail region is scarcely interrupted. If the worm is mul- 
tiplying by fission it may have as many as sixty segments. 
The first segment differs from the others in appearance. 
This difference may be due to its position and modified func- 
tion. The well-developed branchial apparatus at the posterior 
end of the body in all probability does not represent a segment, 
for in cases of fission it is not fully formed until many seg- 
ments have been marked off anterior to it. The growing zone, 
in which are located the cells corresponding to the teloblasts 
of the embryo, lies just anterior to this branchial area. The 
