$ 287. TUE CRUSTACEA. 845 
each of the four anterior pairs of feet, and one only on the last pair. 
With these Crustacea, moreover, the organs have no connection with the 
movable basal joint of the feet; but, on the other hand, most of them 
are inserted on the base itself of the respiratory cavity above this joint. 
Many Macrura, which have numerous branchiae, are those exclusively 
which have one of these organs inserted on the coxa of the feet.“ As 
to their structure, these organs vary also very much. Usually, they have 
the form of a long, acutely-pointed pyramid with a solidly-attached 
base, the axis of which is formed in its whole length by a shaft tray- 
ersed by an arterial and venous canal, and covered by numerous thin 
lamellae or cylindrical filaments, the size of which decreases gradually 
towards their apex. 
§ 287. 
Many terrestrial Isopoda have a branchial apparatus, the organization of 
which is entirely peculiar, and distinctly indicates a pulmonary respira- 
tion. With Porcellio, and Armadillidium, there are four white spots on 
the two anterior pairs gf the branchial opercula. These spots communi- 
cate with as many cavities which ramify like vessels. They are situated 
between the two plates of these four opercula, and are filled with air. At 
the base of each of these opercula there is a narrow opening through 
which, when these cavities are compressed, the air will escape, and then the 
white spots disappear. 
18 The branchiae are fewest with the Brachyura, 
and Caridoidae ; among these last, Crangon and 
Alpheus have only six in each respiratory cavity, 
and Palaemon and Hippolyte seven. Uca, also, 
has only six on each side, while with the majority 
of Brachyura, namely, Portunus, Grapsus, 
Thelphusa, Gecarcinus, Pisa, Maia, Cancer, 
&c., there are eighteen in all, the two anterior 
pairs of which are usually only feebly developed 
and belong to the two pairs of posterior foot-jaws, 
while the others are in general (Mata, Cancer, 
Lupea, &c.) so aggregated at the anterior part 
of the bottom of the respiratory cavity, that the 
space corresponding to the last two pairs of feet 
appears gill-less. The majority of the Brachyura 
have fourteen branchiae on each side, and these 
organgeare even more numerous with various 
Macrura. Thus, I have counted eighteen with 
Astacus, Homarus, and Palinurus; two of 
which, with Palinurus, and Astacus, are in con- 
nection with the middle, and three with the pos- 
terior foot-jaw; while with Homarus, this last 
has also three branchiae, but the second foot- 
jaw has only a rudimentary one. As to the 
other branchiae, there is, in these three genera, 
a branchia inserted on the coxa of the four anterior 
feet. Above each of these same feet are other 
branchiae disposed, in couples; with Astacus, and 
in threes above,the fourth foot, with Homarus, and 
above the second, third and fourth, with Pali- 
nurus ; while above the last foot that is gill-less, 
there is only a single branchia. With Nephrops, 
there are twenty branchiae on each side, and with 
Scyllarus, twenty-one. See, for the number and 
disposition of those organs with the Decapoda, 
Duvernoy, in Cuvier’s Legovs d’Anat. Comp. 
VII. p. 393. 
19 The various forms of the branchiae of the De- 
capoda may be reduced to two types. The first, 
the less common, exists with many Macrura, for 
example with Scyllarus, Palinurus, Gebia, and 
Homarus. The shafts of their branchial arches 
By these means, these animals are undoubtedly in 
support numerous cylinders set together in a 
brush-like manner. In the figures which 4udouin 
and Milne Edwards (Ann. d. Sc. Nat. XI. 1827, 
Pl. XXIX. fig. 1, Pl. XXX. fig. 2, Pl. XXXI.) have 
given of the branchiae of Homarus, this structure 
may be easily seen. With Astacus, the cylinders are 
much less numerous, and disposed only on two of 
the sides of the branchial shaft, — giving it a pin- 
nate aspect; and those which are inserted on the 
coxae are terminated by a thin, multiplicate Jamelli- 
form dilation, which has completely the structure 
of a branchial lamella (Suckow, loc. cit. p 59, Taf. 
X. fig. 1, 2, 25, 26, Taf. XI. fig. 5, 6; Brandt, 
Medic. Zool. II. Taf. XI. fig. 23). With Homarus, 
and Palinurus, also, the coxae have an analogous 
plate inserted close by the side of the coxal 
branchia ; but it is of a leathery consistence and 
covered with numerous hairs, so that it cannot 
participate in the function of respiration, but is 
probably only a septum to separate the different 
groups of branchiae. Aristeus, which has six- 
teen branchiae on each side, differs widely from 
the other Macrura in having its penniform bran- 
chiae composed of a shaft from which pass off 
right and left numerous curled filaments whose 
convex border is covered by tufts of very delicate 
thick-set branchial cylinders (Duvernoy, Aun. d. 
Se. Nat. XV. 1841, p. 104, Pl. V.). The second 
type is formed by these branchiae to the shafts of 
which adhere at right angles numerous thin sume- 
times rhomboidal, sometimes spheroidal lamellae, 
contiguous, aud decreasing in size towards the apex 
of the shaft. This type occurs especially with the 
Brachyura, the Anomura, and with Galithea of 
the Macrura ; also of the Caridoidae, with Palae- 
mon, Hippolyte, Alpheus, Penaeus, Crangon, 
&c.; see Audouin and Milne Edwards, Ann. d. 
Sc. Nat. XI. 1827, Pl. XX VI. and X1. 1839, Pl. 
III. fig. 1, Pl. IV. fig. 1,4 (Maia, Ranina, Palae- 
mon) ; also Kréyer, loc. cit. Tab. I.-V. (Hippo- 
lyte), and Joly, loc. cit. p. 71, Pl. ILL. fig. 24 
(Caridina).. : 
