390 



DECAPOD A. 



commenced, together with 

 the atrophy of the palp or 

 Nauplius appendage. 



Between this and the 

 next observed stage there is 

 possibly a slight lacuna. The 

 next stage (fig. 215) at any 

 rate represents the com- 

 mencement of the Zosea 

 series. The cephalo-thoracic 

 shield has greatly grown, 

 and eventually acquires the 

 usual dorsal spine. The pos- 

 terior region of the body is 

 prolonged into a tail, which 

 is quite as long as the whole 

 of the remainder of the body. 

 The four appendages which 

 were quite functionless at the 

 last stage have now sprouted 

 into full activity. The region 

 immediately behind them is 

 divided (fig. 215) into six 

 segments (the six thoracic 



FIG. 215. PBOTOZO^A STAGE OF PS. Segments) without append- 



( After Fritz Miiller.) ages, while somevv hat later 



the five anterior abdominal 



segments become indicated, but are equally with the thoracic seg- 

 ments without feet. The mode of appearance of these segments 

 shews that the thoracic and abdominal segments develop in regular 

 succession from before backwards (Glaus). Of the palp of the 

 mandibles, as is usual amongst Zosea forms, not a trace remains, 

 though in the youngest Zosea caught by Fritz Miiller a very small 

 rudiment of the palp was present. The first pair of antenna? is un- 

 usually long, and the second pair continues to function as a biramous 

 swimming organ ; the outer ramus is multiarticulate. The other 

 appendages are fully jointed, and the two maxillipeds biramous. On 

 the dorsal surface of the body the unpaired eye is still present, but on 

 each side of it traces of the stalked eyes have appeared. Frontal 

 sense organs like those of Phyllopods are also present. 



From the Protozoasa form the larva passes into that of a true Zoaea 

 with the usual appendages and spines, characterised however by 

 certain remarkable peculiarities. Of these the most important are 

 (1) the large size of the two pairs of antennae and the retention of its 

 Nauplius function by the second of them ; (2) the fact that the 

 appendages of the six thoracic segments appear as small biramous 

 Schizopod legs, while the abdominal appendages, with the exception 

 of the sixth, are still without their swimming feet. The early appear- 



