THE METAMORPHOSES OF CRUSTACEA 73 



The Shrimps and Prawns of the tribe Caridea are 

 mostly hatched as zoeae, and pass through a " schizo- 

 pod" stage comparable to that of the Lobster, in 

 which they swim by means of exopodites on the legs. 

 Some of the Prawns belonging to the tribe Penaeidea, 

 however, have a still more remarkable metamorphosis, 

 which is very important on account of the resem- 

 blance of the earlier stages to those of the lower 

 Crustacea. Fritz M tiller discovered in 1863 that 

 Penceus is hatched from the egg as a Nauplius 

 (Fig. 29, A), a form of larva which was previously 

 known among the Copepoda, Branchiopoda, and 

 Cirripedes. The nauplius, unlike the larvae which 

 we have been considering, has an unsegmented body t 

 and has only three pairs of limbs. The body is 

 pear-shaped in outline, and near the front end is 

 seen the median eye, sometimes called, from its 

 presence in this type of larva, the " nauplius-eye "; 

 the paired eyes are not yet developed. The three 

 pairs of limbs are shown by their later development 

 to be the antennules, antennae, and mandibles ; the 

 first pair are unbranched, the second and third 

 divided into exopodite and endopodite. It is in- 

 teresting to notice that the antennas and mandibles, 

 which in the adult animal are so widely different 

 that it is difficult to trace any resemblance between 

 them, are in the nauplius almost identical in form. 

 Further, the antennae, instead of being placed in 

 front of the mouth as in the adult, lie on either side 



