LORICATA. 281 



(>»/", mf") were similarly reduced at a still earlier stage. The 

 segments carrying the fourth and fifth ambulatory limbs and those 

 of the abdomen become less distinct. 



The youngest hatched Phyllosoma (Figs. 129 and 130) very closely 

 resemble the oldest embryonic stages. The clear, transparent body 

 is flattened out like a leaf, and divided into the three sections just 

 described. The anterior (cephalic) section, which is usually ellipsoidal 

 or oval in outline, carries at its anterior end the two pairs of antennae 

 and the stalked eyes, while the Nauplius eye (oc) lies just above the 

 brain. The mouth lies almost in the middle of the ventral surface, 

 surrounded by the mandibles and first maxillae ; the reduced second 

 maxillae (rnx") have shifted further back. There is, in the Phyllo- 

 soma of Scijllarus (Fig. 129), no trace of the first maxillipedes, 

 whereas, in Palinurus, these are present as vestigial prominences. 



The thoracic region (Figs. 129 and 130) somewhat resembles a 

 Vjroadened disc, and carries the maxillipedes and ambulatory limbs. 

 The two anterior pairs of these limbs (the second and third maxilli- 

 pedes) in the youngest Phyllosoma of Scyllarus are uniramose and 

 five-jointed, while the three anterior ambulatory limbs consist of six 

 Joints and carry exopodites. The rudiments of the fourth and fifth 

 ambulatory limbs, together with the segments to which they 

 belonged, have almost entirely disappeared. In the youngest Phyllo- 

 soma of Palinurus (Fig. 130), on the contrary, the third maxillipede 

 has an exopodite, and the fourth and fifth pairs of ambulatory limbs 

 are found as minute buds. 



The thoracic region of the body is originally simply joined on 

 posteriorly to the anterior cephalic section. Later, however, the 

 dorsal surface of the cephalic region grows back over the thorax, 

 thus forming the dorsal shield, while the thorax itself gives rise 

 principally to the " sternal plastron." 



The abdomen is a short, indistinctly -segmented, rudimentary 

 appendage ending in two furcal processes. Between these, lying 

 at the posterior end of the body, is the anal aperture, which only 

 secondarily takes up a ventral position through the fusing of the 

 basal parts of the furcal processes. This position of the anus recalls 

 that described in Penaeus (p. 267) and Astacus (p. 157), and shows 

 that the Phyllosoma, in the development of the posterior end of tlie 

 body, has retained a peculiarity of an earlier larval stage [Protozoaea 

 of Penaeus). 



The metamorphosis of the Phyllosoma consists in the appearance 

 (or rather reappearance) of the missing body-segments and pairs of 



/^ 



