THE DEVELOPMENT OF THE PODOPHTHALMIA. 301 



oval, u n segmented body with a single frontal eye, a large 

 labrum, and three pairs of natatorial appendages — it is in fact, 

 to all intents and purposes, a JVauplhcs. The JVauplius-torm 

 next develops a rounded tergal shield, or carapace ; the first 

 and second pairs of appendages, remaining, long, become the 

 antennules and the antennae ; while those of the third pair, 

 their bases enlarging at the expense of the rest of the append- 

 age, become the mandibles. Four pairs of appendages sub- 

 sequently appear behind the mandibles. The hinder three 

 pairs are bifurcated and become the two pairs of maxillas and 

 the first and second maxillipedes. Behind these again are 

 five pairs of short lamellar processes, which eventually are 

 converted into the rest of the thoracic appendages. The six 

 somites of the abdomen are long and distinct, and the last 

 ends in two setose processes. They are at first without ap- 

 pendages. In this stage (Fig. 77, J5), which answers to the 

 so-called Zocea-form of other JPodophthalrnia, the principal 

 locomotive organs are the antennae and antennules, and the 

 resemblance to an adult Copepod is so striking that it may 

 be termed the Copepod-st&ge. Next, the antennae, diminish- 

 ing in relation to the rest of the body, cease to be the prin- 

 cipal organs of locomotion, and the rapidly-elongating abdo- 

 men assumes that function. The stalked double eyes, which 

 made their appearance in the Copepod-stage, become more 

 fully developed. The jointed exopodite of the antenna is re- 

 placed by a single plate. The greatly-enlarged thoracic limbs 

 are provided with an endopodite and an exopodite, as in the 

 Schizopoda, the branchiae are developed from them, and the 

 abdominal appendages make their appearance. This may be 

 termed the /Schizopod-st&ge (Fig. 77, C). Lastly, the me- 

 dian eye vanishes, the exopodite of the locomotive thoracic 

 limbs disappears, and the larva assumes all the characters of 

 the adult JPeneus. 



In the great majority of the JPodophthalrnia the embryo 

 undergoes as remarkable a metamorphosis after it leaves the 

 egg. This fact was first indicated by Siebold, afterward 

 demonstrated by Vaughan Thompson, whose observations 

 have been confirmed and extended by many more recent ob- 

 servers, notably by Spence Bate 1 and Claus. 2 But the stages 

 of this metamorphosis differ from those observed in JPeneus in 



1 " On the Development of Decapod Crustacea." (Philosophical Transac- 

 tions, 1857.) 



2 " Zur Kenntniss der Malakostracenlarven." (Wiirzburg " Naturwissen- 

 schaftliche Zeitschrift," 1861.) 



