FOLSOM: MOUTH-PARTS OF ANURIDA MARITIMA. 93 
post-rétinennes, la lame ganglionnaire, le chiasma externe, la masse 
médullaire externe, le chiasma interne et la masse médullaire interne. 
“Toutes ces parties, si nettement caractérisées, se retrouvent sans 
modification chez |’Insecte; il n’est done pas douteux qu’il existe au 
moins pour cette premiére région du ganglion optique similitude com- 
pléte entre les deux types que nous cherchons a4 comparer. . . . Cette 
similitude a été reconnue par tous ceux qui se sont occupés de ce sujet 
(Berger, Bellonci, Carriére et moi)... . . En somme, au point de vue 
des parties dont nous venons de parler, il n’existe que des différences 
bien peu importantes entre l’Insecte et le Crustacé: chez le premier, les 
deux lobes cérébraux sont trés rapprochés et se soudent sur la ligne 
médiane ; chez le second, ces mémes parties (appelées balles supérieures) 
sont écartées, chacune d’elles étant logée dans le pédoncule oculifére 
correspondant.” 
Packard ’98, p. 51) says, “Hence the ocular segment, 7. ¢, that 
bearing the compound and simple eyes, is supposed to represent the first 
segment of the head. This, however, does not involve the conclusion 
that the eyes are the homologues of the limbs, however it may be in 
the Crustacea.’’ As Viallanes has proved the equivalence of protocere- 
brum and optic nerves in insects with those of Crustacea, and others 
have shown that the compound eyes of both groups are constructed 
alike, even to the number of retinal elements, it is proper to infer that 
the compound eyes of the two groups are homologous. 
The protocerebrum of Collembola and Thysanura agrees in develop- 
ment and structure with that of other insects and also with decapod 
Crustacea ; the facetted eyes of Hexapoda and Crustacea are likewise 
homologous. 
Labrum and Clypeus. 
The labrum is chiefly interesting because it has frequently been held 
to represent a pair of primary appendages. 
At Stage 1 (Plate 1, Figure 1; Plate 2, Figures 8, 8%, lbr.) the 
labrum (really clypeo-labrum) is a median hemispherical papilla anterior 
to and distant from the bases of the antennz ; at no period does it give 
evidence of a paired origin. 
At Stage 2 (Figure 2), while the distances between the labrum and 
mandibles is precisely the same as in the preceding stages, the antennz 
are inserted beside the oral region of the upper lip; the latter is globular 
and flattened against the egg shell. 
