374 RUTH B. ROWLAND 
Wax models of the unoperated right pronephros of PN 7 and 
the corresponding organ in PN 7 d were constructed by means 
of the Born method, at a magnification of 200 (figs. 18 to 21). 
Unlike the normal model, to which reference has already been 
made in an earlier section, these two are reconstructions of the 
lumen of the tubules without enclosing walls. The model of 
the kidney of the operated embryo not only showed a consider- 
able increase in the thickness of the tubule as contrasted with 
that of the normal, but its length is also appreciably greater. 
This was determined by taking the average of five measure- 
ments. A flexible but inelastic cord was pinned along the sur- 
face of the wax for its entire course, and its length thus recorded. 
On each measurement the cord was pinned along a different sur- 
face, so that the data would be of a representative nature. For 
the model of the normal kidney the average length was found 
to be 155 cm., at a magnification of 200, with a probable error 
of ±0.181: for PN 7, 188 cm., at a magnification of 200, with a 
probable error of ±0.155, showing an increase of 21 j^er cent 
over the normal condition. 
Microscopic examination of the tubules showed the walls in 
the normal organ (PN 7 d) to be relatively thick and made up of 
cuboidal cells. The hypertrophied tubules (PN 7) were thinner 
walled proportionately, the cells often flattened and elongated, 
and the lumen strikingly larger than that of the unoperated 
specimen^'' (figs. 22 and 23). Outline drawings were made of 
the outer and inner boundary of the walls of the hypertrophied 
and of the normal tubules at a magnification of 600 (figs. 11 and 
12), A non-elastic cord was then pinned at frequent intervals 
along the inner lines, removed and measured, and the circum- 
ference obtained. Five different sections were used at different 
levels in each case, and in each section from three to five tubules 
were measured, makmg a total of twenty-one measurements for 
each kidney. The average measurement obtained for PN 7 d 
^^ In a series of experiments reported by Detwiler ('18), the pronephros was 
often carried along in the transplantation of the limb rudiments. The enlarge- 
ment of the undisturbed pronephros and its contrast with the normal condition 
may also be seen on examination of his plates (Jour. Exp. Zool., vol. 25, 1918, 
pi. 3, figs. 18 and 19). 
