302 



THE ANATOMY OF INVERTEBRATED ANIMALS. 



the apparent absence of the first or JSTauplius condition. Pos- 

 sibly, however, this is represented by a delicate cuticular in- 

 vestment which the larva throws off soon after leaving the 

 egg. It then corresponds with the later form of the Copepod 

 stage of Peneus, and is termed a Zocea. The Zocea has a 

 short carapace, often provided in the median frontal and dor- 

 sal regions with long spine-like prolongations. There is a 

 median simple eye between the lateral sessile faceted eyes, a 

 pair of antennules, a pair of antennae, a pair of mandibles, 



Fig. 73.— Development of Carcinus mcenas.—A, Zoaa-stiige. B, Ifegalopa-etage. C, 

 Final state. (After Couch.) 



and two pairs of maxillae ; in short, all the appendages of the 

 head. Of the appendages of the thorax, the first two pairs 

 are well developed, and terminate in an exopodite and an en- 

 dopodite. But behind these, which become the first and the 

 second pair of maxillipedes, only short rudiments of the six 

 remaining pairs of thoracic appendages are to be found, and 

 the somites of the long abdomen have no appendages at all. 

 Subsequently these make their appearance, the posterior tho- 

 racic members increase in size, the eyes become raised upon 

 short peduncles, and the larva resembles one of the lower 

 Macrura. The carapace next becomes broader, and its spines 

 shorter, while the ambulatory thoracic limbs take on the 

 characters of those of the adult, the bifurcated first and sec- 

 ond pairs becoming metamorphosed into the first and second 

 maxillipedes. The abdomen becomes relatively short and 



