. Text-book de l'embryologie. L'embryologie. VIII 213 AETHEOPODA Ce stade est représenté par le Zoaea les larves de Caridea, Anomura, et Braohyura. Le Zoaea est transformée par plusieurs mues ; d'abord dans un Metazoaea, dans lequel les rudiments des appendices de l'abdomen et de l'entraver de segments du thorax apparaissent ; deuxièmement dans un soi-disant " Mysis " stade, dans lequel, en règle générale, les segments du thorax entraver fourchue ours hmbs conçu pour aider à la natation, et dans lequel la première des annexes du thorax ont tendance à devenir quelque peu diminué en taille et dégradées de la position d'locomot

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. Text-book of embryology. Embryology. VIII AETHEOPODA 213 This stage is represented by the Zoaea larvae of Caridea, Anomura, and Braohyura. The Zoaea is transformed by several moults; first into a Metazoaea, in which the rudiments of the appendages of the abdomen and of the hinder segments of the thorax appear; secondly into a so-called " Mysis " stage, in which, typically, the hinder segments of the thorax bear forked hmbs designed to assist in swimming, and in which the first appendages of the thorax tend to become somewhat diminished in size and degraded from_ the rank of locomotor organs of prime importance to that of maxilhpedes. This Mysis larva, as its name implies, is of such obvious ancestral significance that no one has ever attempted to deny that it represents a Schizopod ancestor. We can, however, even here trace the work. Fig. 160.—" My.sis " larva of Homarus americanus, lateral view. (After Herriclf.) ex^-ex7, the seven exopodites borne by seven of the thoracic legs. of the same modifying tendencies which have obscured the ancestral significance of the Nauplius and the Zoaea. In such of the Nephrops- idea as do not complete their development within the egg-shell (cf. Homarus, the lobster, and Nephro'ps, the Norway lobster) the larva emerges in the Mysis condition, with this difference, that the abdominal appendages are at first quite suppressed. In the Loricata, of which the rock-crayfish, Palinurus, and the square-nosed lobster Scyllarus are the best known representatives, the larva emerges from the egg-shell in a singularly modified Mysis stage (Fig. 161). In this larva the thorax is broad and flat and of a glassy transparency; the abdomen, though distinctly divided into segments, is very small and has no rudiments of appendages. The -thorax has only six of the eight pairs of appendages which it should possess if normally developed, and of these, those representing the first two pairs of maxilKpedes are small but those represen

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