the Mouth in Sucking Crustacea. 5 
- The appendages of the mouth are consequently prolonga- 
tions of the pleure of the head. In many Crustacea more or 
less marked pleural folds may be observed, one fold for each ap- 
pendage, indicating that the head is composed of as many rings 
as it possesses appendages of the mouth. 
The appendages of the mouth (oral limbs) consist typically 
of the following parts :— 
(1) An articular fold near the base, the hinge (cardo). The 
corresponding articular fold at the base of the legs (or the 
limbs organized for locomotion) has been called “ trochantin.” 
In those insects where the coxe at their base are surrounded 
by sockets, the trochantins form the condyles of the coxe, being, 
as well as the latter, free of the epimeron. 
(2) A stem (stipes), corresponding to the coxze of the locomo- 
tive limbs, which is developed in proportion to the require- 
ments of the lobes, its destination being to carry the latter and 
to accommodate the muscles by which they are moved. 
(3) Three free lobes, at the end of the stem, of which the 
two innermost (mal) serye for subdividing and handling the 
food and are therefore modified in accordance with the na- 
ture of the food. ‘The third and outer lobe is the continuation 
of the limb as such, and corresponds to those divisions of the. 
locomotive limbs which follow the coxa. When it is elongated 
and jointed, or shaped as a leg, it is denominated palpus ; and 
its destination is then either to carry organs of sense, to pro- 
duce currents in the water about.the mouth, to cleanse the 
organs of the mouth, to serve as instrument of prehension, or 
some other such function. 
4. A fundamental difference between Insects and Crustacea 
is now to be observed, in the relations of the first pair of oral 
appendages to the side pieces of the skull. 
Crustacea the mandibles do not exceed that point of de- 
_ velopment which is attained by the other appendages of the 
mouth, and consist like these of hinge, stem, and lobes. 
Their flexors are also, as far as the head is not united with 
the body, attached to the hypostoma, and their movement is 
an oscillation, which has for its axis the whole exterior margin 
of the stem, and which sometimes is regulated by an imper- 
_ fect articulation at the exterior and posterior corner of the 
stem. 
In Jnsects, on the contrary, both hinge and stem coalesce 
with the pleure of the head, and their proper muscles are not 
at all developed. ‘The middle lobe alone remains, and articu- 
lates with the side pieces of the skull by an upper and a lower 
condyle, whilst its muscles fill a great portion of the side 
piece. The inner-lobe is only very rarely developed, and is 
