60 
CLAPAREDE ON TOMOPTER1S ONISCIFORMIS 
>j 
advanced stage of the life of Tomopteris than in the earlier (compare figs. 1 and 6 of 
Plate LXII. vol. xxii.) ; and we have found that this difference results from a gradual 
increase in their proportional length, which hears a constant relation to the stage of deve- 
lopment attained by the body. . In an example of this type which we believe to be one of 
the earliest yet met with (fig. 14, PI. VII.), these second antennae (ft, b) were very short, 
and presented a much nearer resemblance to the ordinary lateral appendages of the body 
than they do at a later period. But the distinction between T. onisciformis and T. qua- 
dricornis is mainly rested by Drs. Leuckart and Pagenstecher upon the absence in the 
former of the pair of cephalic appendages borne by the latter, between the " frontal horns 
and the "second antennae; " these, which were designated in the former memoir as the 
" second pair of horn-like appendages," will now be spoken of by us as the first antenna, 
since it is clear that they have more relation to the pair of appendages immediately 
behind them than to those in advance of them. Por, in common with the " second an- 
tennae," they are setigerous, each of them bearing two setaj within its terminal portion 
(fig. 6) ; and in the early form just now alluded to, in which the " frontal horns " were 
entirely wanting, these first antennae were of such a length as to be the principal append- 
ages of the head (a, a, fig. 14). A careful study of the successive stages of the develop- 
ment of Tomopteris, in fact, makes it obvious that these first antenna are to be con- 
sidered as larval, and the second as characteristic of the adult ; for the former progres- 
sively diminish in relative size, and at last (in most cases) disappear altogether, whilst 
the latter progressively increase both absolutely and relatively. In the stage represented 
m fig. 1, Plate LXII. (vol. xxii.), which seems to correspond to the T. quadricornis of 
L euckart and Pagenstecher, the setigerous portion of the first antennae is separated from 
the basal by a constriction which suggests the idea of an articulation (PI. VII. fig. 6. a) ; 
about the time when the caudal appendage begins to be developed, the setigerous portion 
usually detaches itself, while the basal part remains as a mere knob or tubercle ; and in 
the most advanced forms, this tubercle is commonly found to have entirely disappeared. 
A vestige of it, however, is still to be seen in some specimens ; and it would appear, 
not only from the observation made by one of us last year, but also from the mention 
oi these appendages by Mr. Huxley (p. 359), who described and figured them as « long, 
curved spine-like processes arising from the ventral surface of the narrow neck," that 
these nrst antennae are occasionally retained even in the stage of advanced develop- 
~ It is obvious, therefore, that no distinction between Tomopteris onisciformis and 
1. quadncorms can be drawn from the presence or absence of the first antennae ; and if 
no other constant and important characters of difference can be specified than such as 
aboHshed 186 * *** reSpective a " es of the specimens, the last-named species must be 
^5,^ ^additional results of our observations, we shall for the most part 
"f^ f °; th ° Sake of convenience, in the order in which they occured to us in 
pioceedmg from before backwards along the body of the animal. 
is b^mtTI d SP -^? S % WMch We mean th0se in which the ca ^ al prolongation 
PI In 2 I 7 "W ^ ^ b6arS ° n its dorsal surface a P air <*<***** epaulettes 
{ n. vxi. n & . 5. a, a), which extend over the edges of the bilobed nervous ganglion. These, 
ment 
