A phylogenetic classification of animals (for the use of students) . ons in structure, some being converted intojaws, others into sense organs, walking legs, swimming legs,and other organs ; while the segments themselves have alsoundergone change, the exoskeleton becoming in many casesfused over large tracts to form a continuous hard covering orcarapace. Some of the metameres at the front of the bodymore or less completely unite with the prse-oral lobe to forma distinct head. The free larval stage known as the Nauplius, is of suchconstant occurrence throughout the Crustacea, though exhib-iting
A phylogenetic classification of animals (for the use of students) . ons in structure, some being converted intojaws, others into sense organs, walking legs, swimming legs,and other organs ; while the segments themselves have alsoundergone change, the exoskeleton becoming in many casesfused over large tracts to form a continuous hard covering orcarapace. Some of the metameres at the front of the bodymore or less completely unite with the prse-oral lobe to forma distinct head. The free larval stage known as the Nauplius, is of suchconstant occurrence throughout the Crustacea, though exhib-iting slight peculiarities in each group, that it is almostcertain that it represents more or less closely a far-backcommon ancestor. The Nauplius of the Phyllopoda (fig. 17),the most nearly primitive group of Crustaceans, is an ovatebody, provided with three pairs of appendages, attached tothe anterior (cephalic) region. These appendages afterwards 48 become the two pairs of antennae and the mandibles. Thefirst pair of antennae are comparatively slight, consist of one. Fig. 17. Phyllopod Nanplius (Apus) when hatched (after Claus). 1, first pair ofantennEe ; 2, second pair of antennae ; 3, mandibles; I, labrum; o, median eye;s, segments of the post-cephalic region of the body. branch only, and are probably sensory organs. Betweentheir bases is placed a large upper lip or labrum, behindwhich lies the mouth. The second antennae are very muchlarger, and are biramous, with a spine projecting from nearthe base inwards towards the mouth. These appendagesare the main organs of locomotion of the Nauplius. Themandibles are rather smaller. They represent the mandi-bular palps of the adult, and are biramous. On the frontof the head is placed a median unpaired eye. The post-cephalic region shews traces of five segments and theirappendages, and in this respect differs from most Nauplii,which are unsegmented. Probably this Phyllopod Nauplius is the nearest formknown to the primitive Crustacean, b
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
