Chilton. — On Thoracic Leys in the Whale-feed . 321 



the Macrura anomala, a group including the majority of the 

 Crustacea generally classed as Anomura, the Rev. T. R. R. Steb- 

 bing says,* ' The fifth pair of legs are generally weak, not fit 

 either for walking, swimming, or grasping food or prey." In 

 many of the free-swimming forms, such as Grimothea, these legs 

 have the joints of the limb folded against one another like the 

 limbs of the letter Z, and the whole appendage is carried at 

 the side of the carapace above the bases of the more anterior 

 legs, and in this position they have the appearance of being 

 quite useless ; and I am not aware that any function has ever 

 been assigned to the fifth pair of legs in this section of. the Ano- 

 mura, though in another family, the Lithodido?, where the fifth 

 pair of legs are slender, chelate, and folded in the branchial 

 chambers, Mr. Stebbing has suggested that they may be used 

 to keep the branchial clear of parasites, and thus be of advantage 

 to the animal. f 



During a short stay at the Marine Fish Hatchery and Bio- 

 logical Station at Portobello, in November, 1904, I had. oppor- 

 tunities of observing living specimens of Grimothea gregaria, 

 and one day while watching a small specimen under the dis- 

 secting microscope I was much interested to see the animal sud- 

 denly unfold the fifth pair of legs, stretch them forward over the 

 anterior portion of the carapace, and with the tuft of setse on the 

 terminal joints carefully brush away extraneous matter from 

 the dorsal surface of the carapace, and particularly from the 

 spaces between the rostrum, the eyes, and the bases of the 

 antennae. The action was quite unexpected, and was almost 

 ludicrously like that of a person engaged in brushing his back 

 hair. For the purpose in question the fifth pair of legs of 

 Grimothea gregaria seem well fitted — they are just long enough 

 when unfolded to reach conveniently to the anterior portion 

 of the carapace; and the two terminal joints (propodos and 

 dactylus), which are bent nearly at right, angles to the pre- 

 ceding joint, and when at rest are curved behind the bases of 

 the fourth pair of legs, are supplied with numerous long setse 

 projecting radially from them, one row of seta? being curved 

 and pectinate, and the whole forming a sort of circular brush 

 specially adapted for sweeping out the spaces between the spines 

 of the rostrum, around the bases of the eye-stalks, &c. These 

 two joints, moreover, form a chela or pincers with the fingers 

 somewhat spoon-shaped, and are doubtless used to pick off 

 substances that cannot be brushed away. 



As the Grimothea gregaria swims rapidly backwards by 

 means of alternate flexions and extensions of its abdomen, 



* "History of Crustacea," p. 149. f *•<>•> P- 155. 



21— Trans. 



