Saag 
7 ra 
4 
a 
1% 
if 
i; 
= 
the Mouth in Sucking Crustacea. 15 
the mazxillipeds at once arrest the attention. The cardo 
(Pl. I. fig. 45, c) is expanded outwards and forwards into a 
large triangular plate, which covers the root of the second pair 
of maxille. The stem is very large, elongated, quadrangular 
(fig. 4 6, s), its underside shghtly vaulted; but the lateral 
or outer portion is boldly arched upwards, so as to embrace 
the cols of the second pair; and the upper surface of the 
stem has near the inner margin a thick Noheitndieal crest 
fitting so accurately into a depression on the corresponding 
side of the middle ridge of the sphenoid plate between this 
ridge and the maxille of the second pair, that the stem by 
these means is kept quite firmly in its position. On account 
of this crest, the stem appears rather thick when detached and 
viewed from the side of the inner margin, which latter is quite 
straight and even, so as to fit in exactly with the correspond- 
ing margin of the maxilliped on the opposite side, to which it 
lies close through the whole of its length. 
The five-jointed palpus of the maxillipeds (p, fig. 4b) is 
of about the same length as the stem. ‘The first joint is very 
short, and is placed transversely in front of the fore end of the 
stem, whilst the four following joints form a bluntly pointed, 
inwardly curved, cup-shaped leat, which rests on one edge, so 
that it inclines a little inwards. The upper (and outer) even 
edge of the leaf fits first into a narrow groove on the inner 
edge of the stem of the mandible, and then passes round the 
mandible and lays itself into the bend between the mandibular 
stem and lobe, whilst the front edge is curved inwards and 
embraces the corresponding side of the labrum. On the in- 
ferior margin of the palpus, near the end of the second joint, a 
couple of small soft hooks are implanted ; and a greater number 
of such are distributed along the margin and along the outer 
side of the following joints. They do not, however, appear as 
hooks, except when viewed from the side, and particularly 
when the palpus is pressed flat; but from beneath or from the 
side, when the palpus is in its natural shape, they are seen 
fore-shortened, and then appear as a row of short thorns along 
_ the margin of the third joint, and as a lump of warts on each 
side of the labrum. 
In this manner the two leaves formed by the palpi, placed 
on edge and bending towards each other, embracing some 
other parts of the mouth, constitute the sides of the sucking- 
tube. Nevertheless a slit remains between them; but this is 
filled up at the bottom by the two very short, conic, com- 
ressed, brevisetose lobes of the maxillipeds, and, further, in 
Bont by the inner lobes of the second pair of maxille, which 
will afterwards be described. 
