THE MAXILLARY FAN 41 
5. Close up to the lower lip, and as little leg-like as 
any of the appendages, are placed the first maxille. They 
are almost always thin and foliaceous, with few joints, and 
those few not easy to distinguish. ‘The pattern is ex- 
tremely variable. ‘The functions are obscure. There are 
sometimes strong fringing spines which may assist in 
dividing the food. There are plumose hairs, some of 
which may be connected with the sense of taste. The 
position of these organs has also suggested that they may 
‘be useful in preventing the escape of food from the 
lateral angles of the mouth.’ It is with these that some 
authors close the number of true cephalic appendages. 
Of those which follow some are frequently, but none with 
the same constancy, developed into mouth-organs. 
6. The second maxillze, when present, have generally 
the same thin flattened character as the first, but their 
structure is often more complicated. Among other pecu- 
harities they have in some of the higher groups a mem- 
branous expansion or large lamina on the outer side, 
frequently termed the flabellum or fan, and compared by 
Milne-Edwards to a ventilating register (see Plate XI.). 
This species of valve is in constant and rapid vibration, in 
most cases forcing the water which has aerated the gills to 
pass out in front, so that a new supply may be introduced 
from behind; but in some crabs (as Dorippe, Ranina, Leu- 
cosia) according to de Haan the water is introduced in 
front, and passes out behind. Huxley supposes that this 
valve may represent the epipod, that is to say, the branch 
which is given off by the first joint of an appendage, or 
else that it may be a combination of the epipod of the first 
joint with the exopod of the second.! Professor Sars re- 
gards it as the exopod,? while Dr. Hansen considers that 
it springs from the third joint.* In those Crustacea which 
have the branchie either not enclosed in a chamber or in 
one remote from the head, this part of the maxilla is either 
absent or rudimentary (see Plates XVI., XIX.). 
1 The Crayfish, p. 170. (The scaphognathite. ) 
2 The Normeyian North Atlantic Expedition Crustacea, p. 21. 
3 Oversigt over de paa Dijmphna-Togtet indsamlede Krebsdy7, p. 193 
note, and p. 252. 
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