No. I.] STUDIES ON LIMULUS. 107 



right angles to the median line and parallel to each other. The 

 homologies can then be more readily made out. The first pair, 

 the chelicerae (Text-fig. i ; PI. VIII, Fig. 3, ap.'), lies almost 

 parallel to the median line, so that the morphologically anterior 

 side faces the median line. They are small chelate appendages, 

 anterior to the mouth, consisting of but three segments, and 

 are regarded as homologous with the antennae of insects and 

 myriapods. 



The next four pairs of appendages (Text-fig. 2), from the 

 second to the fifth, serve as ambulatory legs and also as masti- 

 catory organs. In the female they are all chelate. In the male 

 the chelae of the second pair of appendages are modified to serve 

 as clasping organs. The propodite is thickened, and its terminal 

 process, which is ordinarily the anterior blade of the chela, is 

 aborted ; the dactylopodite, or posterior blade of the chela, 

 is curved anteriorly so as to be opposed to the aborted end of 

 the propodite. 



Each of these appendages is composed of six joints, of which 

 the fourth is double, being formed by the fusion of the meropo- 

 dite and the carpopodite. The proximal margin of the coxopo- 

 dite (Text-fig. 2, l-cox.) is much thickened, and forms a structure 

 of complicated outline which has been called by Lankester the 

 "entocoxite." If the coxopodite be examined from the proximal 

 side, the entocoxite may be clearly seen (Pis. VI and VII, Figs. 

 I and 2, ent.^'^). The outer portion is divided by chitinous bars 

 into three spaces filled with areolar tissue containing numerous 

 nerve endings. These spaces appear as slight swellings or knobs, 

 probably highly sensory, upon the outer extremity of the base of 

 the coxopodite. The inner, or median, portion of the coxopodite 

 is modified to form a mandible (Text-fig. 2, maji.) which projects 

 over the mouth and bears numerous, inwardly projecting spines 

 provided with gustatory buds. The mandibles of the third, 

 fourth, and fifth pairs of appendages bear an inner detached por- 

 tion (Text-fig. 2, i.man.) furnished with a small flexor muscle. 

 These inner mandibles have been called by Lankester the " epicox- 

 ites." They are also supplied with spines and gustatory buds.^ 



^ For the structure of the gustatory buds of the mandibles, and also of similar 

 buds in the chelae, see Patten, " Morphology and Physiology of the Brain and Sense 

 Organs of Limulus," Quar. Jouni. Micr. Set., 1893. 



