KKSriK’ATOKY OKGANS ]N AlfANK/E. 
9 
I found it quite impossible to obtuin uu accurate idea of 
the rudimentary luug-books and trachea} iii the embryos, 
except by means of reconstructions, of which extensive use 
was made. For the complicated lung-books a large number of 
the ordinary reconstructions wiih wax tablets were made 
(thickness of sections 5‘82 q, of wax tablets 2 mm.; magnified 
343’7 diameters), but for the simpler trachea} the following- 
method was employed: 
A sheet of transparent paper is placed over another of white 
paper ruled with a series of parallel lines 2 mm. apart. 'J'he 
width of the organ to be reconstructed maguified the required 
number of times (343‘7 times for sections 5-82 /i thick), is 
measured with a])air of compasses in each section and marked 
off on the parallel lines, each of which represents a section. 
When all the sections have been marked in this way on the 
transparent paper the outlines of the organ will be obtained 
in their coiTect proportions. This method is much quicker 
than the other and very suitable for reconstruction in outline 
from transverse sections of any bilaterally symmetrical organ 
of simple form, such as the embryonic trachete in the later 
stages (figs. 28 and 29). By drawing a line down the middle 
of the paper at right angles to the parallel lines to re])re- 
sent the median line of the body, and marking each transverse 
section symmetrically on each side of this line, the symmetiy 
of the reconstructed organ will be preserved. 
If. (iKNEKAL OltlEXTATiON. 
Lung-books. — A typical well-developed lung-book of a 
Dipueumonous spider has the following }>arts (figs. 20 
and 21) ; 
(1) A more or less transverse spiracle (•'■-p.) or stigma 
placed laterally at the junction of the ventral and lateral 
surfaces of the second abdominal segment along its hind 
margin (text-fig. 1). 
(2) A short flattened tube leading forwards from the 
spiracle into the body in a slightly upward and medial direc- 
