288 SIR JOHN LUBBOCK ON THYSANURA. 
seen, that there is only one pair of spiracles. He considers, however, that they are 
situated in the thorax, close to the place of insertion of the anterior legs, while I think 
they are in the head. 
I will not be so bold as to say that there certainly is no spiracle in the place indicated 
by Von Olfers; the animal is so small and so inconvenient for dissection, that I will 
not venture to make a positive assertion in opposition to one who has evidently worked 
with much care and skill. Nevertheless I think he has been misled by the fact that 
at this part the tracheze are held in place by the rather large branch given off to the 
anterior leg. I think I have traced all the tracheæ up into the head, and that the only 
spiracles possessed by Smynthurus are situated in the head, at the place where it is 
attached to the body. 
As regards the other species, I differ still more from M. Nicolet and Von Olfers. I 
have examined Tomocerus plumbeus, as well as species of Achorutes, Lepidocyrtus, Iso- 
toma, Lipura, and am satisfied that they do not possess any tracheal system answering 
to the descriptions either of Nicolet or of Von Olfers. 
| THE GENERATIVE ORGANS. 
I have already described the generative organs of the Smynthuride in my first paper. 
Those of Tomocerus, which may be taken as representing the Poduride, are very simple, 
and in both sexes consist of two tubes, commencing near the anterior end of the abdomen. 
They widen gradually as they pass back, and open on the ventral side of the posterior 
segment behind the base of the spring. 
NERVOUS SYSTEM. 
Tomocerus. 
In the head are two ganglions, the supra- and infracesophageal, which are connected 
by two short commissures, between which the œsophagus passes as usual. 
The remainder of the nervous system consists of three ganglia, lying in the thorax and 
first abdominal segments. The posterior ganglion is much the largest and is double, 
The hinder portion is somewhat square-shaped, and sends off several strong nerves 
backwards. 
Smynthurus. 
Nicolet was unable to discover the nervous system in the linear Thysanura while that 
of the globular species appeared to me much more difficult to make out. As described by 
him, Smynthurus has, like Tomocerus, two ganglia in the head, and three in the thorax. 
The supracesophageal ganglion is large, and gives off the nerves for the eyes and the 
antennee. : 
MUSCULAR SYSTEM. 
Smynthurus. 
Muscles of the Caudal Appendage. (Plate XLV. figs. 9-11)—So far as I am aware, 
no naturalist has hitherto given any account of the muscular system in the Thysanura. 
