: 1886.] i so-called “Spiral Thread” of Trachee. 44i 
primitive tracheal membrane, and the so-called “ spiral thread” is 
formed by parallel thickenings of the nuclei composing the 
secondary layer of nuclei, and which become filled with the chitin 
secreted by these elongated nuclei. The middle portion of the 
tenidia, immediately after the molt, is clear and transparent, with 
obscure minute granules, while the nuclear base of the cell is 
filled as usual with abundant granules, and contain a distinct nu- 
cleolus. 
The origin of the tenidia is also well shown by Fig. 2, which 
is likewise a longitud- 
inal section of a 
+ trachea at the point 
of origin of a branch. 
The peritracheal 
membrane or ecto- 
trachea (ectr) is com- 
posed of large granu- 
lated nuclei; and 
within are the more 
t transparent endotrach- 
eal cells; at 7 are 
fragments of the molt- 
ed tenidia. The new tænidia are in process of development at 
t; at base they are seen to be granulated nuclei, with often a dis- 
tinct nucleolus, and sending a long slender, transparent, pointed 
Process along the inside of the trachea. These unite to form the 
chitinous bands or so-called spiral threads. 
The tenidia I have found to be separate, independent, solid 
rings, More or less parallel and independent of each other. The 
Supposed spiral arrangement I believe to be an optical illusion. 
The tænidia of a main branch stop at the origin of the smaller 
branches, and a new set begin at the origin of each branch. This 
fact also shows conclusively that the chitinous bands are not 
Spiral. Nor do the tenidia at the origin of the branch pass en- 
trely around the inside of the peritoneal membrane; in the axils Gs 
y are short, separate, spindle-shaped bands. -o 
The tænidia are usually thin, flat, but often slightly concavo- : sf a 
convex, the hollow looking towards the center of the trachea. Io 
Vave been unable to find any forming incomplete hollow rings or 
tubules, like the pseudotrachea of the fly’s tongue figured and a 
Fic, 2. Origin of the teenidia. 
EI S eS 3 C a a i a ERELT RA 
x $ 
