Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 Fig. 117. Nauplius of a Copepod (Cyclops), a h c Appendages. Form of the Body. § 183. Among the Crustacea tlie simplest stage of tlie Arthropod body- is seen in the Nauplius-form (Fig. 117). The unsegmented body carries several pairs of appendages. The body only becomes segmented by a gradual process of gem- matiouj which has many points of resem- blance to the process which brings about metamerism in most of the Annulata. The most anterior portion of the body of the Nauplius which carries
Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 Fig. 117. Nauplius of a Copepod (Cyclops), a h c Appendages. Form of the Body. § 183. Among the Crustacea tlie simplest stage of tlie Arthropod body- is seen in the Nauplius-form (Fig. 117). The unsegmented body carries several pairs of appendages. The body only becomes segmented by a gradual process of gem- matiouj which has many points of resem- blance to the process which brings about metamerism in most of the Annulata. The most anterior portion of the body of the Nauplius which carries the first appendages forms the cephalic segment; the posterior part becomes the last metamere; new meta- meres are formed between these two, on which appendages similarly sprout. In this way an organism composed of a larger number of metameres is gradually formed (Fig. 118); the com- plication of which, so far as it is due to metamerism, is the product of a gradual process. This development of the form of the body pre- dominates in the Ento- mostraca; it corresponds, probably enough, to the phylogeny of these Crus- tacea, which therefore may be referred back to an unsegmented condi- tion. IntheMalacostraca this process of the forma- tion of new metameres can be made out in a few cases only, and the rudi- mentary body ordinarily consists at the very first of a larger number of metameres. The con- secutive formation of metameres is here com- pressed ; and the same hajapens in the Poecilo- poda and in most Tra- cheata. Although this might seem to remove any doubts as to the common origin of the Arthropoda, it is not of so much weight rig. 118. Larva of Br an chip us stagnais. (second stage), ale Appendages, mx Rudiments of the maxillae. J' Caudal fork, o Eye (after C. Clans).
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