21 



the next ecdysis the limbs undergo practically no change, but 

 the larva acquires its characteristic spines. It is now called a 

 zoea. During the so-called zoea stages the posterior limbs are 

 growing, but t3rpically remain rudimentary until the ecdysis 

 which reduces or obliterates the thoracic spines and broadens 

 the carapace in the formation of the megalopa. In these respects 

 the Brachyura are in agreement with the Thalassinidae and the 

 Stenopodidae, and some of the Anomura only differ in that after 

 the first few ecdyses the third pair of maxillipeds attain develop- 

 ment, becoming, like the first two pairs of maxillipeds, swimming 

 legs. It is in this state, also, that is to say, with eight pairs of 

 limbs, that the Caridea are hatched typically. In all these cases 

 it may be suggested that the name protozoea should be given to 

 all the pre-megalopa stages, in other words, there is no zoea stage. 



As has been noted in the case of the Penaeidea, the physio- 

 logical difficulties in the formation of the last two pairs of limbs 

 of the thorax, that is just where the abdomen commences, leads 

 to a hesitation in the development, resulting sometimes in the 

 suppression of the limbs. The effect is seen in other groups. The 

 zoea stage may be thus defined as larvae with pereiopods or with 

 all the segments and limbs complete to the tenth, eleventh, 

 twelfth or thirteenth. We may thus include the phyllosoma 

 stages of the Loricata with eleven pairs of appendages, still retain- 

 ing for convenience, however, the name phyllosoma, the erichthus 

 larva of the Stomatopoda, with ten pairs of appendages, as well 

 as the larvae of the Homaridae, which are typicalh^ freed with 

 all the limbs to the thirteenth fully formed. Even the first stage 

 of the lobster although it possesses thirteen pairs of limbs has 

 been styled a protozoea. 



The successive stages give time for the appendages not 

 developed at hatching to grow, and as has been apparent, it is 

 convenient to define the stages in succession when groups of the 

 limbs attain a functional condition. The nauplius has three 

 pairs of limbs, and during the metanauplius ecdyses, while the 

 nauplius limbs retain their prominence, the next four or five 

 limbs are gradually reaching their full development. As soon as 

 this has been accomplished the larva may be called a protozoea. 

 A further series of ecdyses give time for the thoracic limbs behind 

 those already developed to become prominent, and when the 



