The Shrimps and Prawns of the tribe Caridea are mostly hatched as zoëæ, and pass through a "schizopod" 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 Penæidea, however, have a still more remarkable metamorphosis, which is very important on account of the resemblance of the earlier stages to those of the lower Crustacea. Fritz Müller discovered in 1863 that _Penæus_ 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 larvæ which we have been considering, has an unsegmented body, 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, antennæ, and mandibles; the first pair are unbranched, the second and third divided into exopodite and endopodite. It is interesting to notice that the antennæ 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 antennæ, instead of being placed in front of the mouth as in the adult, lie on either side of it, and each has at its base a hooked spine which projects inwards and serves for seizing particles of food and passing them into the mouth; the antennæ of the nauplius, in fact, serve as jaws, while it is only later that the mandibles take on this function. [Illustration: FIG. 29--LARVAL STAGES OF THE PRAWN--_Penæus_ (SEE PLATE IV.). × 45. (After F. Müller.) A, Nauplius; B, young zoëa; C, older zoëa; D, early "schizopod" stage]