6 Prof. J.C. Schidédte on the Structure of 
then always fixed to the middle lobe. As there is no stem, 
there cannot be any mandibular palpus. 
The development of the articulate archetype from the crus- 
tacean stage to the insect stage is here the same as that of 
the vertebrate archetype from fish to mammalia; and this 
analogy may also be traced in several other respects. In both 
these series of animals the cephalization is furthered by this, 
that the principal organ for the handling of the food gradually 
loses its form of limb by the coalescence of its basal divisions 
with the side pieces of the skull; in this way these latter gain 
additional space for accommodating the nervous system, whilst 
the movement of the jaws at the same time increases in power, 
because the muscles of the basal divisions of the limb disap- 
pear, and all the space on the increased side pieces of the skull 
is available for the muscles moving the remaining terminal 
aN of the jaws. The cephalization of the oral limbs of 
ertebrata (the lower jaw) may be observed in different stages 
in reptiles and birds; the same is the case with the mandi- 
bles of Articulata. One of the intermediate stages, found in 
the lower Insects, with imperfect or no metamorphosis, and in 
sucking Insects, has recently been pointed out by Dr. Meinert 
in his paper on Campodee *. | 
5. In the hedriophthalmous or fourteen-footed Crustacea 
the first ring of the trunkT is connected with the skull, and as 
it ceases to be moveable its dorsal part (pronotum in Insects) 
disappears, whilst the ventral and lateral parts (prosternum and 
epimera prothoracica) still remain as separate pieces between 
the head and the second ring, because they carry a pair of 
limbs, the fore legs, which enter into the service of the mouth, 
and therefore assume the shape of maxille. These mouth- 
feet or maxillipeds have their coxee in proximity to each other 
in the middle, and correspond thus far to the labium of Insects, 
that they afford a cover for the mouth from beneath, and assume 
a similar foliaceous and laciniated shape. Fabricius and his 
school therefore called them labium, as their morphologic inter- 
pretations were based only on the shape and use of the parts. 
Next to the coalescence of the stems of the mandibles of 
Insects with the side pieces of the skull, there is no more im- 
portant point of difference between the structure of the mouth © 
in Insects and in hedriophthalmous Crustacea than precisely 
this conformation of the maxillipeds simulating a labium. 
Covering as it does the mouth from beneath, the existence of this 
false labium renders unnecessary any other cover ; consequently 
* Translated in Ann. & Mag. Nat. Hist. ser. 3. vol. xx. p. 361. 
+ In this paper the expressions “ trunk” and “ tail” stand for “thorax” 
and “abdomen” in the terminology of Milne-Edwards and others. . 
