268 CRUSTACEA. 



and two truncated processes provided with setae at the posterior 

 end of the body (furcal processes). This stage greatly resembles 

 the Metanauplius of Lucifer (Fig. 118 B, p. 258). Like the latter, 

 it possesses a massive, helmet-shaped upper lip. The three pairs of 

 Nauplius limbs appear shifted somewhat forward, and four pairs 

 of bud-like limb-rudiments have arisen. The third Nauplius limb 

 shows an important alteration, a thickening of its basal portion being 

 evident as the rudiment of the masticatory blade of the future 

 mandible, while, from the two swimming rami, the living contents 

 have been withdrawn, an indication that these parts will be cast 

 off in the next moult. Near the eye, the paired frontal organ (Fig. 

 122 B), which also occurs in the Zoaean series, can be recognised 

 as a small, conical projection. 



The next stage observed is the Protozoana (Fig. 122 B), with well- 

 developed, more or less rounded, cephalo-thoracic shield, seven pairs 

 of limbs and an unsegmented abdomen (ab) terminating in distinct 

 furcal processes. The antennae are still locomotory organs. The 

 first antenna (1) is divided up into four joints. On the posterior 

 antenna (2) a three-jointed endopodite and a four-jointed exopodite 

 can be recognised. The upper lip is helmet-shaped and marked by 

 a spine which points forward, this is also found in the larvae of the 

 Sergestidae. The mandibles are now palpless, toothed, masticatory 

 blades. The maxillae agree to a great extent in shape with those 

 figured for Lucifer (Fig. 119 B and C, p. 260). In the first maxilla, 

 two inwardly projecting cutting blades can be recognised on the 

 protopodite, there is a jointed endopodite and a leaf-like exopodite 

 provided with setae. The second maxilla resembles the first in 

 shape, but has four blades on the protopodite and a somewhat longer 

 endopodite. The two anterior pairs of maxillipedes (Z, II) are 

 developed as biramose swimming limbs. At the base of the 

 succeeding (thoraco-abdominal) region of the body, transverse rings 

 mark a division into six segments (those bearing the third maxillipede 

 and the five ambulatory limbs, III-VIII). The position of the 

 anal aperture is worthy of mention ; it is, at this stage, exactly 

 terminal, lying between the two furcal processes, and only later 

 shifts to the ventral side of the telson. The presence of three 

 pairs of hepatic outgrowths from the intestine is already evident. 

 The heart, which is situated at the anterior extremity of the 

 thuraco-abdomen, has only one pair of ostia (1). At the anterior 

 margin of the cephalo-thorax, the rudiments of the paired eyes are 

 visible as swellings in close contact with the frontal organ. 



