40 MICROSCOPICAL STUDIES. 



pigment representing the unpaired simple eye, of the same structure 

 as that of the Squilla larva*. 



The mouth is situated on the under side of the head, midway 

 between the front and hinder edges, and is surrounded by an upper 

 -lip or labium (PI. vi, Fig. 2), two stout mandibles, and two pairs of 

 maxillae, the first large, with two appendages and working inwards 

 in the same plane as the mandibles ; the second pair, on the contrary, 

 are small and rudimentary and appear not to function. 



Of the maxillipeds the first pair is non-existent, showing not 

 the slighest trace : a very peculiar fact and characteristic of Scyllarus, 

 distinguishing from the youngest Phyllosome ofPalinurus where this 

 appendage is just visible as a tiny cylindrical process.* The second 

 however, though slender, can be easily resolved into six joints, while 

 the third is more than thrice this length and proportionately stouter. 

 Behind this are three enormously elongated spider-like limbs, the 

 .true ambulatory legs or pereiopods ; each is six jointed the terminal 

 one claw-shaped and reminding one sharply of the similar appearance 

 of this joint in the adult. The first and second ambulatory limbs are 

 biramous, for there springs from the further end of the second joint 

 in each, a paddle-functioning jointed and plumose appendage which 

 represents the exopodite. The third is unbranched, but a knobbed 

 projection on the second joint indicates where the exopodite is about 

 to sprout forth. In older larvae the third maxilliped also develops a 

 plumose branch. Four pairs of limbs, the third maxillipeds, and the 

 six pereiopods are the only appendages of the thorax at this stage, 

 but as age advances and repeated moults take place other pereiopods 

 appear at the point between the base of the abdomen and the third 

 pereiopod ; these in turn assuming the biramous character of the 

 first formed. 



* In this statement I give the accepted view (Dohrn, Zeitschr. fur iviss. Zool. 

 1870). My own examination of the young larvae, points rather to the missing 

 appendage being the second maxilla and not the first maxilliped. Undoubtedly 

 one or other is missing, for between the first maxilla and the second maxilliped, 

 there is but one organ, and the reason why I think this to be the first maxilliped is 

 that the somite it belongs to, is clearly defined and shows no trace of having another 

 somite between it and the equally well defined somite bearing the second maxilliped 

 (see Fig. 2). On the other hand, the region in front of the somite bearing this 

 uncertain appendage, and between the latter and the first maxilla, is extensive, and 

 bears no appendage. The shape too, of the uncertain limb, is in favour of my view ; 

 it consists of a stout, rather fusiform basal joint, bearing a tiny terminal joint from 

 which spring four long and highly plumose hairs. Now in the Phyllosome of 

 Palinurus which possesses both second maxillae and first maxillipeds, Cunningham 

 (Journ. Mar. Biol. Assn., New Ser., Vol. II, No. 2, p. 147) describes the former as 

 rather large and foliaceous and gives the figure of a distinctly biramous limb ; while 

 the latter he speaks of as being each a simple, small but distinct conical stump, 

 a description much more fitting the organ in the Scyllarus larva, than that of 

 the second maxilla, for it is in nowise foliaceous, nor yet biramous. Not having 

 examined the embryo nor yet any advanced Phyllosomes of Scyllarus, I cannot 

 however give my view as more than an opinion. 



