. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE CRUSTACEA. 433 I, the sides n being iu ere at tbe erefore be tide which lediau Hue ig. 195, ol) u function, ints of the ' of large rax. Each )f a papilla sal joint of )ular organ d complex ry function brick-red " indicating ;s (coxae) of apening on f the opev- hed paired astoraosiug numerous situated ou -When the able reseni- ,ffinity Avitli 3 Palaeozoic remains of have beou 3 Trilobites. six pairs of ly those of md oarlike, probably serving for swimming. Th
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE CRUSTACEA. 433 I, the sides n being iu ere at tbe erefore be tide which lediau Hue ig. 195, ol) u function, ints of the ' of large rax. Each )f a papilla sal joint of )ular organ d complex ry function brick-red " indicating ;s (coxae) of apening on f the opev- hed paired astoraosiug numerous situated ou -When the able reseni- ,ffinity Avitli 3 Palaeozoic remains of have beou 3 Trilobites. six pairs of ly those of md oarlike, probably serving for swimming. The abdomen was com- posed of twelve segments, the anterior six of which were much more massive than the others and bore five pairs of platelike appendages on whose posterior surface were the branchiae. The terminal segment bore a spine or fiulike structure. Such a form as this, represented by the genus rterygotus (Fig. 198), presents strong similarities to Zimulus and also to the Scorpions, bearing out the numerous similarities of structure occurring between Zimidus and those forms. This side of the affinity may be postponed, however, until the next chapter, and the comparison of Limidus with the Crustacea discussed here. Its chitinous cuticle, its jointed and biramous appendages, and its branchial respiration show similari- ties to the Crustacea, as do also the form of the heart and the compound eyes. Whether or not the coxal gland is comparable to the shell- gland is at present uncertain, but the other similarities are sufficient to justify the recognition of a Crusta- cean origin for Limulus. It iormi^ YmAm.âPterygotus angliens indeed a connecting link between the ^^'â °"* Nicholson). Crustacea and the Arachnida, presenting probably on the whole more affinities with this latter group than with the former. Since, however, a Crustacean ancestry is probable, a com- parision of the appendages of Limulus with those of a repre- sentative of the ancestral group ought t
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