1897.] Microscopy. 747 
mounted, later transferred to wax sheets. Buta pencil point is first 
made on the dorsal side of the sketch in the median plane, and some- 
times also one in the same plane 
on the outline of the surface of 
some central organ, such, for in- 
stance, as the neural cord (r 
and m, figs. 1 and 2). 
The photograph or sketch of 
the embryo is then enlarged 
upon a piece of bristol-board to 
correspond precisely with the 
magnification of the sections and 
the enlarged figure cut out with 
a sharp knife (fig. 2). If only 
an enlarged model of the en- 
tire embryo is desired, the re- 
mainder of the process is very 
short and simple. One has only 
to arrange the sections of wax 
representing the sections of the 
* embryo within the bristol-board 
outline one after another and 
then smooth off outer surface 
Fig. 1. with a warm modeling tool. 
If the sections are cut at right 
angles to the dorsal guide line of the right angle as well as to the 
median plane, the process will be easier to follow, for then the wax sec- 
tions can be put in place with reference to this line. And if a model of 
only a portion of the embryo is desired, the proper place of the wax 
section in the bristol-board outline may be readily determined from the 
known thickness of the sections and the numbers in the series of the 
section with which the reconstruction is begun, by simply measuring 
off the proper distance on this dorsal guide line. For example, if the 
sections be 20» thick, the magnification 100, the number of sections 
100, and one desires to reconstruct the middle region of the embryo, 
beginning with the thirtieth section, the distance will be 20 x 30 x 100 
or 
If, as is usually the case, one desires a reconstruction of an internal 
organ, the process is somewhat more complicated. Then one will have 
need of the second guide point (m) already mentioned as on the surface 
of one of the principal or centrally located organs. In cutting out of 
