4io 
TRANSFORMATIONS OF INSECTS. 
parasitic true insect — is very degraded in its structures and develop- 
ment ; and the forms classified as Goniodes are also remarkable 
for their defective organisation, as well as for the presence of a claw 
upon the antennae of the males. The philosophical naturalist may 
ponder with interest upon the absence of the metamorphoses in 
these parasitic creatures, and consider their evident anatomical, 
and therefore classificatory relation with those spiders which have 
tracheae as their respiratory organs ; and he must be struck with 
the anatomical relations of these groups with the other insects that 
undergo incomplete or imperfect metamorphoses. 
The Thysanura or skip tail tribe are small insects which are 
better known on account of the beauty of their microscopic body 
scales than for any interesting habits or instincts. They do not 
undergo metamorphosis, and are wingless. 
Sir John Lubbock’s careful researches have resulted in his 
being satisfied that in the genus Smynthurus there are tracheae 
for respiratory purposes, and that they communicate with the 
external air by means of spiracles, which are not situated along 
the margins of the thorax, but in the head, where it is attached 
to the body. 
