. Quarterly journal of microscopical science. location and lipomerism mayoccur without fusion of tegumentary plates, and with, onthe contrary, a dwindling and eventual atrophy of suchplates. The general considerations as to metamerism set forthabove will enable us to proceed to a consideration of thecharacters which distinguish the various groups of Arthro-poda, and to justify the classification with which we started. The Theory of the Arthropod Head.—The arthropod 544 E. RAY LANK ESTER. head is a tagma or group of somites whicli differ in numberand in their relative position in regard to the
. Quarterly journal of microscopical science. location and lipomerism mayoccur without fusion of tegumentary plates, and with, onthe contrary, a dwindling and eventual atrophy of suchplates. The general considerations as to metamerism set forthabove will enable us to proceed to a consideration of thecharacters which distinguish the various groups of Arthro-poda, and to justify the classification with which we started. The Theory of the Arthropod Head.—The arthropod 544 E. RAY LANK ESTER. head is a tagma or group of somites whicli differ in numberand in their relative position in regard to the mouth, indifferent classes. In a simple Chastopod (fig. 1) the headconsists of the first somite only; that somite is perforated bythe mouth, and is provided with a prostomium or pra3orallobe. The prostomium is essentially a part or outgrowth ofthe first somite, and cannot be regarded as itself a gives rise to a nerve-ganglion mass, the prostomial the marine Cl)a3topods (the Polychteta) (fig. 2) we find Fig. 1. Fig.
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Keywords: ., bookcentury1800, bookdecade1850, bookpublisherlondo, bookyear1853
