> 
“ spirals of the proper tracheæ ” are ‘‘ crenulated thickenings of the intima,’ 
~ Strated the true nature of the pseudotrachez of the fly, His criticisms of Chuns 
442 Nature and Origin of the so-called “Spiral Thread,” etc.{May, 
described by Professor G. Macloskie.! It seems to me that the 
function of the tenidia is like that of the cartilaginous rings of 
the trachez of vertebrates, 7. e, to keep the air-passage open so 
that the air may pass to the cells at the end of the trachea. All 
the figures of the spiral thread hitherto published I believe to be 
incorrect. In Guyon’s work on Pulex penetrans they are repre- 
sented to form a loose spiral, and so they appear at first glance 
under a low power in the trachez of the common flea of the cat. 
But on close examination, in an excellent preparation, the so-called 
spiral thread is a series of independent parailel tænidia, the spaces 
between them being wider than usual. In Fig. 3, from a prepa- 
Fic. 3.—Stigma and trachea of Pulex, 
ration kindly presented to me by Mr. Justin Spaulding, æ repre- 
sents one of the first abdominal spiracles and the trachea arising 
from it; 4 the fifth; and c one of the last abdominal spiracles and 
its trachea. When the trachea bends or contracts in diameter the 
taenidia become less parallel, and a spiral appearance is produced. 
In the last pair the tænidia are remote from each other. 
In a preparation of one set of the salivary glands from the 
head of the honey bee, given me by Mr. Spaulding, the common 
duct is much like a trachea, having similar tenidia, and here they 
are observed to be parallel, independent bands. 
The sections of Datana were made for me by Professor H. C. 
-Bumpus of Olivet College. 
1 Thus far I find myself unable to agree with Professor G. Macloskie that = 
tort 
the teenidia are really tubular. In his valuable and suggestive article, “ The Struc- 
ture of the Trachez of Insects (AMER. NAT., XVII, 567), I believe he has demo 
- 
views and figures I believe, in the main, to be correct, but thus far I am unable to 
convince myself that the “ external fissure ” of the tenidia in the figure he copies 
from Chun, whose original essay I possess, is really such ; it appears to be a new 
_ tenidium in process of formation previous to molting. 
