SIR JOHN LUBBOCK ON THYSANURA. 287 
longueur; ils sont insérés immédiatement au-dessus du rétrécissement pylorique; leur 
longueur égale à peine la moitié de celle du ventricule chylifére; du reste, leur extrême 
ténuité et leur peu de consistance ne m'ont pas permis de les étudier en détail" *. Von 
Olfers also describes them as “ filiformia, tenerrima ;" but he only saw four. When the 
Malpighian vessels are very numerous, it is naturally difficult to count them; but as 
they are in this group so few, Nicolet can certainly not have seen them very distinctly 
when he remained in doubt as to the number. | 
For my own part I have examined Orchesella fastuosa, the species in which they are 
figured by Von Olfers, as well as Tomocerus plumbeus, Smynthurus, and other species, but 
have never been able to satisfy myself that any such organs really exist. | 
The intestine has, in Tomocerus, a length of about $; of an inch. It is straight, and 
of even diameter. It is strongly muscular, being provided throughout its whole length 
with transverse muscles, which lie close together, and are about 1350 of an inch in 
diameter. 
Respiratory Organs. (Plate XLV. figs. 7, 8.) 
The condition of the respiratory system of the Thysanura is a question of much interest. 
Nicolet describes a series of spiracles situated at the sides of the superior arches of the 
abdomen. The tracheæ extend, according to him, in an undulating line from the head 
to the tail, each undulation corresponding to a segment, and sending out on the one side 
a short branch to the corresponding spiracle, and on the other a number of branches 
which ramify over the different organs of the body. There are also on each side six 
pneumatie sacs which lie longitudinally, communicate by a short duct with the main 
tube, and give out from the posterior end two branches, one of which goes to the side of 
the body, passing under the principal trache a. He figures the tracheæ arranged in this 
manner in A. fimetarius, and, though not expressly saying so, appears to regard the 
description as applicable to all the Podwrelles (Thysanura). | 
In my first memoir in the * Linnean Transactions” (vol. xxiii. p. 429), on the contrary, 
I have described the tracheæ of Smynthurus as opening by two spiracles in the head, 
opposite the insertion of the antennz—that is to say, on the lower side of the head, if 
it is placed with the antennæ and eyes upwards, or on the back part when it is in its 
natural perpendicular position. 
As regards Achorutes and the allied genera, Von Olfers repeats the statements of 
Nicolet. His own observations were made on Smynthurus oblongus, Tomocerus plumbeus, 
and Orchesella fastuosa. In these he found the respiratory system formed on one plan. 
They have two spiracles only; and these are situated on the inferior side of the thorax, 
close to the first pair of legs. From each spiracle start three principal trunks, one of 
which goes forwards, one upwards, and one backwards. The first two are immediately 
divided into a great number of branches, which are extremely narrow. The other passes 
to the middle line, lies close to the corresponding trachea of the other side, without, how- 
ever apparently uniting with it, and then also breaks up into a number of fine branchlets. 
I have again examined Smynthurus, and can only confirm my previous statements. 
Von Olfers, without being acquainted with my memoir, agrees with me, as we have 
* L. c. p. 47. 
VOL. XXVII. 2Q 
