PENEIDEA AND CARIDEA LARVAL HISTORY 



i6r 



the hir.unous thoracic limbs are completed the abdominal biramous 

 pleopods are added, beginning from in front backwards. Thus 

 tlie Mysis stage (Fig. 109) is reached, which resembles in all 

 particulars the adult condition of the Schizopoda. The adult 

 l^rawn develops from this stage by the loss of some or all of the 

 exopodites on the thoracic pereiopods. 



Some of the Peneid larvae take on very peculiar forms, e.g. 

 the Zoaeae of the Sergestidae,^ which often develop the most 

 wonderful spines all over the body. 



Fig. 109. — Mysis stage in the development of Penens, sp. A.2, 2nd antenna ; Ab.6, 6th 

 abdominal appendage ; T, telson ; Tli, the biramons thoracic appendages. (After C'lau.s.) 



The Caridea have a greatly abbreviated metamorphosis, the 

 larva hatching out at a late Zoaea stage with all three pairs of 

 maxillipedes fully formed and with a fully segmented abdomen. 

 The succeeding thoracic limbs are added in order from before back- 

 wards, though the sixth pair of pleopods appear precociously as in 

 the Peneidea. The other swimmerets do not begin to develop 

 until the thoracic limbs are complete. Some Caridea show a yet 

 more abbreviated metamorphosis, e.g. the freshwater Palaemoiietes 

 varians of S. Europe, which hatches out at the Mysis stage. 



We see, therefore, in the metamorphosis of the Macrura 

 several apparently primitive features. In the first place, a free 

 swimming Nauplius stage is preserved in certain forms, identical 



^ Challenger Jieporis, xxiv., 1881. 

 VOL. IV M 



