94 
MR. W. K. BROOKS OK LUCIFER : 
pointed out (‘ Untersuchungen / &c., p. 15), that the Decapod metastoma is morpho¬ 
logically a pair of appendages ; that it has been formed by the simplification and union 
of structures homologous with the limbs; and that this pair of appendages was originally 
furnished with a body-somite and a pair of ganglia. Claus’s reason for the homology 
is the resemblance between the Decapod Protozoea and the larva of Phyllopods and 
Copepods, and the manner in which these parts are developed in the Nauplii of Lucifer 
and Euphausia seems to be an additional reason for accepting his view. 
The first maxilla. 
This appendage is rudimentary during the Nauplius stages, but, as shown in 
fig. 21, Mx. 1 , it is represented by a pair of buds several hours before birth. 
In the Protozoea and Zoea series it has the form shown in fig. 46, which was drawn 
from the appendage of a larva in the last Zoea stage. Its characteristics are developed 
gradually, and it is somewhat simpler during the earlier Protozoea stages than it is in 
fig. 46. Fig. 30 shows it as it appears in the first Protozoea when seen from the 
outside. It consists of a basal portion (fig. 46) made up of two joints (l and 2), which 
carries a short obscurely-jointed endopodite (en) and a scaphognathite (sc). In my 
description of this and the other mouth parts of Lucifer I have accepted Claus’s 
homology (‘ Untersuchungen,’ &c., p. 16), and regard the two basal joints as the 
equivalent of the basal portion of the antenna, or of one of the thoracic limbs ; the 
jointed palpus as the homologue of the inner ramus of the antenna, or the limb proper 
of one of the thoracic appendages; and the scaphognathite as the homologue of the 
exopodite of one of the thoracic appendages, or of the antennae. In all these appen¬ 
dages the exopodite is shorter than tbe endopodite, unjointed, and set with long hairs, 
the plumose character of which is well marked. The scaphognathite of the maxilla 
agrees with the exopodite of the second antenna and of the other appendages in this 
respect, while the palpus of the maxilla agrees with the endopodite of the second 
antenna, and with that of tbe mandible of tbe Nauplius and with the thoracic limbs of 
the adult Lucifer , in consisting of several joints with one or more, usually simple, 
hairs at each joint. 
The inner edges of the basal joints of the maxilla carry cutting hairs, and the 
second joint is largest. The endopodite carries five long slender hairs which are simple 
in the earlier and plumose in the later stages. The scaphognathite carries three hairs 
which are equal and simple in the earlier Protozoea , but plumose in the Zoea, where one 
is very much longer than the other two. 
The structure of this appendage undergoes extremely little change from the time it 
appears in the Protozoea to maturity. In the Schizopod larva (fig. 52) the second 
basal joint (2) has become much larger than the first (1), and its cutting hairs are more 
numerous than before; a small slender plumose hair has made its appearance on the 
edge of each joint. The endopodite (en) is obscurely three-jointed, and the scaphogna¬ 
thite (.sc) has only two long plumose hairs. 
