nigta. 3° PENBEIDEA AND CARIDEA—LARVAL HISTORY 161 
the biramous thoracic limbs are completed the abdominal biramous 
pleopods are added, beginning from in front backwards. Thus 
the Mysis stage (Fig. 109) is reached, which resembles in all 
particulars the adult condition of the Schizopoda. The adult 
Prawn 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. 
I 
Fic. 109.—Mysis stage in the development of Penews, sp. A.2, 2nd antenna; Ad.6, 6th 
abdominal appendage ; 7’, telson ; 7h, the biramous thoracic appendages. (After Claus.) 
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 Palaemonetes 
varians of 8. 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 Reports, xxiv., 1881. 
VOL. IV M 
