SIR JOHN LUBBOCK ON THYSANURA. 295 
mouth. Although, however, the Poduridæ and Smynthuridæ certainly do possess 
mandibles, still their mouth differs very greatly from that of all other mandibulate 
insects. 
. The points which we have principally to consider in relation to the classification and 
position of the Thysanura are :—the absence of metamorphoses; the absence of wings; 
the presence or absence of trachew; the structure of the mouth; the saltatory caudal 
appendage; and the ventral tube. 
The last-mentioned organ, though observed by most of the preceding writers, has not, 
I think, attracted the attention it deserves. It is, in fact, the true characteristic of the 
group. The absence of wings and of metamorphoses is not peculiar to the Thysanura; in 
fact the presence of metamorphoses is closely connected with that of wings. To the 
tracheæ we must not attach too much importance; for though absent in the great 
majority of the group, they occur in Smynthurus. The peculiar mouth-parts of the man- 
dibulate genera are entirely absent in Anura; and the caudal appendage is wanting in 
the Lipuride. | 
Thus, then, the ventral tube is characteristic as being general to the true Thysanura, 
and still more so as being peculiar to them ; for I know of no similar organ in any other 
group of Articulata. The presence of tracheæ, the structure of the mouth, and the abdo- 
minal appendage, all indicate a wide distinction between the Lepismidæ and the Podu- 
ridæ, and, when considered in conjunction with the fact that the ventral tube is absent 
among the former, force us to the conclusion that the two groups are much less closely 
allied than has hitherto been supposed. 
We must, indeed, in my opinion, separate them entirely from one another; and 1 would 
venture to propose for the group comprised in the old genus Podura the term Collembola 
as indicating the existence of a projection or mammilla enabling the creature to attach or 
glue itself to the body on which it stands. 
We now come to consider whether it should be classed among the Insecta, or whether 
Lamarck was right in separating it from that great class. Taking each of the character- 
istic points separately, we begin with the absence of metamorphoses. To this we must 
not attribute too much importance. There are species of Orthoptera and of Neuroptera 
which are almost in a similar position. So, again, as regards the absence of wings, the 
same argument holds good : in all orders of insects there are wingless species. Moreover, 
although it may seem paradoxical to say so, the character of an organ is of greater classifi- 
catory value than the absence of it. Thus, for instance, we have cattle and deer without 
horns, but no cows have deers’ horns or vice versá. So the presence of four wings is 
absolutely peculiar to the Insecta; but some insects have only two wings, and in all 
the large orders there are'species without any wings at all. The absence of wings is there- 
fore no conclusive evidence against classing the Collembola amongst the Insecta. 
The absence of trachese is more significant. That of wings involves only inability 
to fly but that of trachee implies that respiration is carried on in a different 
manner. The importance, however, of the difference is reduced to a minimum, because 
L. c. vol. iii. p. 378. 
YOL. XXVII. 2R 
