THE DECAPODA 



293 



Athich persist through several of the later stages. The next stage 

 observed is the Protozoea (Fig. 170, B), in which the seven pairs 

 of limbs already indicated are well developed ; the carapace covers 

 the anterior part of the body ; the abdomen, which has a furcate 

 termination, is still unsegmented, but the six posterior thoracic 

 somites are defined, though very short. The mandibular jxdp has 

 quite disajipcared (to reai)pear at a later stage), and the first and 

 second thoracic appendages are biramous swimming-limbs. At this 

 stage the rudiments of the paired eyes begin to appear beneath the 



Early stages of Pcnaeus. A, nauplius ; H, early 

 I'rotozoea -stage. (After F. M tiller, from Kncy. 

 Brit.) 



carapace, there are three pairs of hepatic caeca, and the heart is 

 developed, though as yet with only one pair of ostia. In a later 

 Protozoea-stage (Fig. 171, A) the five anterior abdominal somites 

 are indicated, the sixth being not yet marked off from the telson, 

 and the rudiments of the third pair of thoracic limbs appear. In 

 the following stage, to which the name of Zoca is given, the paired 

 eyes become free from the carapace and are movable, the carapace 

 begins to grow out into a median rostral spine, the third pair of 

 thoracic limbs are biramous, and rudiments of the remaining five 

 pairs are present. The first five pairs of abdominal appendages 

 (Fig. 171, B) are present as very small buds, but the sixth pair 



