^287. 



THE CRUSTACEA. 



3i5 



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 trav- 

 ersed by an arterial and venous canal, and covered by numerous thin 

 lamellae or cylindrical filaments, the size of which decreases gradually 

 towards theii' 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 of 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. By these means, these animals are undoubtedly in 



18 The branchiae are fewest with the Brachyura, 

 and Caridoidae ; among these last, Crangon and 

 Alpheus have only six in each respii'atory cavity, 

 and Palaemon. and Hippolyte seven, f/ca, also, 

 has only six on each side, while with tlie 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 (Maio, 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 

 organs are even more numerous with various 

 Macrura. Thus, I have counted eighteen with 

 Aatacus, Homarus, and Palinurus ; two of 

 which, with Palinurun, 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 al)ove the last foot that is gill-less, 

 there is only a single branchia. With Nepkrops, 

 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 Leijons d'Anat. Comp. 

 Vir. p. 393. 



I'J 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 



support numerous cylinders set together in a 

 brush-like manaer. In the figures which Audouin 

 and Milne Edwards (Ann. d. Sc. Nat. XI. 1827, 

 PI. XXIX. fig. 1, PI. XXX. fig. 2, PI. XXXI.) have 

 given of the branchiae of Homarus, this structure 

 may be easily seen. With Astacus, the cyUnders 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 lamelh- 

 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 nimierous 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 oU' 

 right and left numerous curled filaments whosi 

 convex border is covered by tufts of very delicat-j 

 thick-set branchial cylinders {Duvernoy, Ann. d. 

 Sc. Nat. XV. 1841, p. 104, PI. V.). The second 

 type is formed by these branchiae to the shafts of 

 which adhere at right angles numerous thin some- 

 times rhomboidal, sometimes spheroidal lamellae, 

 contiguous, and 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, PI. XXVI. and XI. 1839, PI. 

 III. fig. 1, PI. IV. fig. 1,4 (Maia, Ranina, Palae- 

 mon) ; also Kroyer, loc. cit. Tab. I.-V. {Hippo- 

 lyte), and Joly, loc. cit. p. 71, PI. 111. fig. 24 

 (Caridina). 



