6 Prof. J. C. Schiodte on the Struct ii7'e 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 cnis- 

 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 

 parts of the jaws. The cephalization of the oral limbs of 

 Vertebrata (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 Campodeee *, 



5. In the hedriophthalmous or fourteen-footed Crustacea 

 the first ring of the trirnkf 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 maxilla. These mouth- 

 feet or maxillipeds have their coxas in proximity to each other 

 in the middle, and correspond thus far to the labium of Insects, 

 that they afibrd a cover for the mouth from beneath, and assume 

 a similar foliaccous 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 iu Ann. & Mag. Nat. Hist. ser. 3. vol. xx. p. 3G1. 

 t In this paper the expressions " trunk " and " tail " stand for " thorax" 

 and " abdomen " in the terminology of Milne-Edwards and others. 



