Archive image from page 769 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana01todd Year: 1836 754 CRUSTACEA. The Loemodipods, the Entomostraca, and the IIaustellate Crustacea present us with instances of this condition, which calls to mind one of the stages through which the embryo of the higher species, whose development is the most complete, is known to pass. Each segment of the body, when it attains its normal condition, consists of two distinct ele- ments : the central or annular portion, and cer- tain appendices which it supports. The central or a
Archive image from page 769 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana01todd Year: 1836 754 CRUSTACEA. The Loemodipods, the Entomostraca, and the IIaustellate Crustacea present us with instances of this condition, which calls to mind one of the stages through which the embryo of the higher species, whose development is the most complete, is known to pass. Each segment of the body, when it attains its normal condition, consists of two distinct ele- ments : the central or annular portion, and cer- tain appendices which it supports. The central or annular portion of the seg- ments of the tegumentary skeleton presents, in its most simple state, the appearance of a com- plete ring, but instead of a single piece it is requisite to count in its composition no fewer than eight, as has been demonstrated by,the inquiries of M. Audouin on the structure of the thorax of insects, inquiries the results of which are immediately and almost wholly applicable to the Crustacea so nearly allied to the insects in their organization. Each ring is divided first into two arcs, the one superior or dorsal, the other inferior or ventral, and each arc may present as many as four elementary pieces. Two of these pieces by being united in the me- Fig. 378. Theoretical figure illustrating the composition of the tegumentary skeleton of Crustacea. 1), Dorsal arc ; t, t, tergal pieces ; e, e, epimeral pieces ; V, ventral arc ; s, , sternal and episternal pieces ; P, insertion of the extremities. dian line constitute the tergum (jig- 378, D) ; the superior arc is completed on either side by two other pieces, known under the name oifiancs or epimeral pieces (Jig. 378, e). The inferior arc presents in its composition an exact counter- part of the superior. Two of the four pieces into which it may be resolved constitute the sternum, situated in the median line, and are flanked by the two episternums. The two arcs thus composed, instead of cohering by t
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