CR USTA CEA ONTOGENY 



391 



Larval history of Penaeus (Order Decapoda, Sub-order Macrura, Family 

 Carididse (Shrimps), Figs. 263 and 264). 



1. Nauplius Stage. A typical unsegmented Nauplius (Fig. 263, A) is hatched 

 from the egg. The body possesses no dorsal shield ; it carries 2 setse posteriorly. 



2. Metanauplius Stage. The dorsal shield begins to form. The 3d pair of 

 Xauplius limbs (mandibular limbs) shows 



the rudiments. of the masticatory ridge. 

 Behind this appear the rudiments of the 4 

 subsequent limbs (maxillre and 2 anterior 

 pairs of maxillipedes). 



3. First Protozosea Stage (Fig. 263, B). 

 The cephalothoracic shield has grown 

 large. The posterior division of the body 

 elongates till it is as long as the anterior 

 part. The 2 pairs of maxillae and the 2 

 anterior pairs of maxillipedes have devel- 

 oped and are capable of functioning ; the 

 latter are biramose limbs with endo- and 

 exopodites. The division which follows 

 behind these is divided into 6 segments 

 without any trace of extremities, and these 

 segments are the rudiments of the 6 pos- 

 terior thoracic segments (III-VIII). These 

 are followed by the posterior body which 

 is not yet segmented and shows no trace 

 of extremities. The mandibular feeler has 

 disappeared. The posterior body ends 

 with two furcal processes. Near the 

 median eye the paired eyes appear. 



4. The Second Protozosea stage (Fig. 

 264, A] is very similar to the first, but on 

 the abdomen the rudiments of the 5 

 anterior abdominal segments (a^-a^) are 

 visible. Behind the 2d pair of maxilli- 

 pedes on the first of the 6 newly formed 

 thoracic segments the rudiments of the 3d 

 pair of maxillipedes appear (III). 



5. First Zosea Stage. The paired eyes 

 stand out as stalked eyes. The 3d pair of 

 maxillipedes has also become biramose. 

 On the 5 subsequent pairs of thoracic seg- 

 ments the rudiments of the 5 pairs of 

 "ambulatory feet" appear (Fig. 264, B, 

 IV- Till). On the segments of the 

 abdomen also formations appear which are 

 probably the rudiments of the pleopoda 

 (ai-cts). In any case the beginnings of the 

 last pair of pleopoda which are destined to 



(H-M) 



FIG. 263. Young larva of Penaeus (after 

 F. Muller). A, Nauplius ; B, Protozoaea. III- 

 VIII, Rudiments of the 3d-8th trunk segments. 

 ab, Abdomen ; 1-5, limbs of the head ; I, II, 

 of the thorax. In all subsequent figures the 

 head limbs are denoted by Arabic, the thoracic 

 limbs by Roman numerals, the abdominal limbs 

 (pleopoda) by i, a^ etc., the telson by t, the 

 exopodite by ex, and the endopodite by en. 



form with the telson the caudal fin, are distinctly visible on each side as bi-lobed 

 formations under the integument. 



6. Second Zosea Stage (Fig. 264, (7). The last pair of pleopoda project freely. 

 On the two pairs of maxillse the small fan-plates (exopodites) have formed. The 5 



