HABIT AND HABITAT IN THE GALATHEIDEA. 93 



ieeble and irregular. The result of the experiments performed on Porcel- 

 lana is surely to show that any recuperative purpose effected by the 

 reversal of the respiratory stream in the Decapods for which such reversal 

 has been proved is fulfilled in Porcellana by the alternate resting and 

 working of the two sides. 



Throughout the Galatheid group we note a praiseworthy striving after 

 cleanliness on the part of its members, which must of course be referred 

 to the habitat of these animals. Apart from the absolute necessity for 

 keeping a clear channel through the branchial cavity, it is of distinct 

 advantage to prevent mud particles from collecting among the hairs of 

 the coxopoditic tufts and near the openings of the branchial cavity itself, 

 and it is clearly the function of the curiously modified thirteenth (last 

 thoracic) appendage to clean and brush these hairs, as well as the back 

 of the carapace. Galathea and Munida especially have need of precaution 

 against the settling of foreign particles in the transverse grooves of the 

 carapace. The ultimate segment of the thirteenth appendage in Galathea, 

 JMunida, and Porcellana, bears hairs which by their structure are peculiarly 

 well fitted for this work of cleaning out chinks and crannies (Plate 4, K), 

 each hair being bent into a kind of sickle-shaped hook, fringed on its 

 inner side with short, pointed teeth, and doubtless constituting a most 

 effective scraper. In one species of Porcellana (P. plafycheles, see Plate 

 7, K, ii), these hairs appear to have suffered degeneration from some un- 

 explained cause (perhaps in connection with the absence of carapace 

 ridges), growing less strongly curved and with blunt teeth. It is notice- 

 able that members of the genus Porcellana (without epipodites) fre- 

 quently thrust this appendage XIII inside the branchial cavity itself, 

 doubtless to clean it — a course of proceeding which Galathea (furnished 

 with epipodites) apparently does not follow. 



The antennules (water-testing organs) and the antennae (which are 

 still important tactile organs in the Galatheidse) must, if they are to 

 retain their sensory function, be kept scrupulously clean, and their 

 cleansing, which frequently takes place, is a process to delight the ob- 

 server. These appendages are bent sharply downward, then the endopo- 

 dites of the third maxillipedes are unfolded, and antennules and antennae 

 are drawn slowly upwards in such a manner as to be thoroughly well 

 combed by the long hairs of these palps, which hairs have the form of 

 strong double-edged saws or combs (Plate 4, 1, i). These endopodites of 

 the third maxillipedes, by the way, exhibit an interesting series of special- 

 izations throughout the group. Their main functions are {a) to gather 



