SIR JOHN LUBBOCK ON THYSANURA. 285 
The explanation of M. Bourlet's mistake, however, is to be found in the fact that an 
antenna once seriously mutilated never regains its normal number of segments. Such, 
at least, has been my experience. It is possible that very young specimens may have 
more complete powers of reparation. I doubt very much, however, whether it is so, 
because I have observed in Chloéon (Ephemera) that the terminal segments of the 
antenna, if once removed, are never replaced (although the antenna continues to grow), 
so that not one specimen in twenty of those which I examined had perfect antennæ 
when the insects were half-grown. 
As illustrating the partial recovery which takes place, I will take the following cases 
from my note-book | 
. On the 11th of April, I removed the terminal portion of the right antenna of a pale 
Orchesella cincta, at the middle of the second segment, as shown in Pl, XLV. fig. 1. On 
the following day the animal moulted, and the mutilated antenna was as in fig. 2, the 
second segment being a little elongated, but not much altered, probably on account 
of the short time which intervened between the mutilation and the moult. On the 
19th of April the antenna was as in fig. 3, and consisted of three segments. The second 
and third were quite unlike those of normal specimens, the second being unusually large, 
and the third, which is normally quite short, being elongated and somewhat club-shaped. 
Subsequently both these segments, and especially the third, elongated somewhat (fig. 4), 
but they made no further approximation towards the nornial form. 
Again, on the 5th June, 1 treated another specimen in the same manner, leaving the 
antenna in the state shown in Pl. XLV. fig. 5. On the 17th June it had moulted, and 
was as in fig. 6. Here, the mutilation having taken place near the extremity of the 
segment and some days before the moult, it will be seen that more change has taken 
place than in the preceding case. The antenna is three-jointed, the two apical segments 
presenting the same peculiarities as in the preceding specimen. Subsequently the ter- 
minal segment elongated as in fig. 7 ; but no further change took place. 
. I made a few more similar experiments with similar results, but was reluctant to 
multiply them too much, being unwilling to cause unnecessary pain, and seeing no 
reason to expect any materially different results. 
It is remarkable that in all these cases the terminal segment acquires a length even 
greater than that which it possesses in normal specimens. This is vell shown also in 
Choreutes. In this genus I have satisfied myself, both by direct experiment, and also 
by watching specimens which I had met with accidentally, that if the terminal seg- 
ment is removed it is never replaced, though the third segment acquires an unusual 
length. I have even seen specimens, under these circumstances, in whieh the third 
segment acquired a length almost equal to that of the third and fourth segments of a 
normal antenna. 
