16 Prof. J.C. Schiddte on the Structure of 
In front the oral tube is closed by the labrum, which hangs 
perpendicularly from the clypeus; this latter is itself in a 
erpendicular position, elongated and arched in front. The 
ier is of semicircular outline, and edged by a thick, soft, 
membranaceous fringe, which is dotted over with small pointed 
warts. 
When the maxillipeds are removed, we observe the short 
prosternum, and in front of it the sphenoid plate, on which 
an elevated ridge is conspicuous along its middle line, which 
becomes gradually thinner towards the apex, besides the sockets 
of the cardo and stem of the maxillipeds, and, finally, the 
second pair of maxille. As we have stated already, a depres- 
sion is observed on either side between the latter and the 
middle ridge of the sphenoid plate, which is filled up by the 
longitudinal crest on the upper surface of the stems of the 
maxillipeds. The consequence is that the stems of the second 
pair of maxille are entirely covered in from beneath by the 
stems and the base of the palpi of the maxillipeds. The 
stems of the second pair of maxille. present the shape of elon- 
gated, inverted-pyriform, thin and uneven saucers, somewhat 
narrowedand flattened towards theirfore ends, which meet across 
the middle ridge of the sphenoid plate, just inside and above 
the second joint of the palpi of the maxillipeds. Their con- 
cavity is, of course, turned upwards towards the under surface 
of the skull; and in the space thus enclosed the maxille of the 
first pair are lodged, with sufficient spare room to insure their 
free movement. ‘T’he maxillary lobes of the second pair are 
small, thin, of rounded outline, at the apex and along the 
inner margin armed with some small, rather soft, hooked 
spines. ‘The rounded outline of the lobes, however, only ap- 
pears when they are unfolded; for in their natural position 
their appearance is very different. The inner lobe is then 
ohecbvads (a*, fig. 45) in the slit between the palpi of the 
maxillipeds, at the inner posterior corner of the second joint ; 
but it is twisted round, so that it is seen foreshortened, and 
the hooks above mentioned seem in consequence to form al- 
together but one thick thorn. The whole anterior margin of 
the outer lobe, on the contrary, is turned back like a collar over 
the anterior margin of the second joint of the maxillipeds. 
The part played by the second pair of maxille in the con- 
struction of the sucking-apparatus is consequently this, that 
their stems are excavated into sheaths for the styliform first 
pair of maxille, and their lobes fill up the remaining gaps 
in the sucking-tube, of which the opening becomes a closed 
circle formed by different elements which can slide over each 
other and are armed with small hooks. | | 
