112 General Notcs. i [ January, 
of paper, each zone corresponding in thickness to a single see 
tion (1™™). a 
A median line would then be drawn at right angles to these 
zones; this line would represent the length of the disc magnified 
20 diameters (100™"). We should next make an outline drawing 
of the first section enlarged the same number of diameters as be 
fore. The width of this drawing and its parts (primitive streak, 
embryonic rim, &c.), could then be indicated in the first zone by 
dots placed at the proper distance on the right and left side of the 
median line. The dots for each succeeding section having beet 
placed in their corresponding zones, nothing further would remait 
to be done, except to connect the dots of corresponding parts it 
the several zones, and shade according to the requirements of the 
ca 
se. f 
If the plane of section is not quite perpendicular to the axis ob 
the object, one has only to determine the angle which the axis 
makes with the plane of section, and draw the median line so that | 
it forms the same angle with the parallel zones. Such a cas 
been clearly illustrated by Krieger. : 
In the construction of sagittal sections, a profi 
: le line (d 
line, &c.), will serve as the ground line. { 
_ roe progress 1 donl 
_ of cilia (or minute hairs) in the air-passages, and the 
line tion of the nasal mucus may (it is also sugge 
