. Animal physiology. Physiology, Comparative; Physiology, Comparative. ANNELIDA, OR LEECH AND WORM TRIBE. 95 lose their eyes and legs, and become fixed for the remainder of their lives. 114. We now pass to the lower division of Articnlata, in which the body possesses no jointed members ; and the animals belonging to this group are for the most part included in the class of Annelida, the Leech and Worm tribe. We here find the body enveloped,—not in a hard casing, formed in distinct pieces united by a flexible membrane,—but in a skin which is altoge- ther flexible, and which gives little indicat
. Animal physiology. Physiology, Comparative; Physiology, Comparative. ANNELIDA, OR LEECH AND WORM TRIBE. 95 lose their eyes and legs, and become fixed for the remainder of their lives. 114. We now pass to the lower division of Articnlata, in which the body possesses no jointed members ; and the animals belonging to this group are for the most part included in the class of Annelida, the Leech and Worm tribe. We here find the body enveloped,—not in a hard casing, formed in distinct pieces united by a flexible membrane,—but in a skin which is altoge- ther flexible, and which gives little indication of a division into segments. The reason of this is evident. In the Articulata possessed of distinct members, the act of movement or progres- sion is accomplished for the most part by these only; and the more they are developed, the less flexible do we find the body. The same principle has been already pointed out in regard to the internal skeleton, or spinal column, of Yertebrata. In Fishes, the motion of the body through the water is accomplished chiefly by its own vibration from side to side, and the spine is very flexible. (§. 98). In Birds, on the other hand, where the motion of the body through the air is effected by the stroke of its wings, the trunk is very strongly knit together, in order to give a firm attachment to the powerful muscles by which they are moved (§. 88). Hence in the Articulated series, it is natural that we should expect to find the covering of the body most soft and flexible, in those lowest tribes, in which there are no separate members for its propulsion. 115. The Class Annelida includes several distinct tribes ; which all agree, however, in the long worm-like form of the body, and in the similarity of the different ganglia of their nerv- ous system. The highest tribe is adapted to live in air as well as in water ; this includes the Leeches and Earth-worms, in both. Fig. 56—Leech. of which we see the division of the body into rings tolera
Size: 4155px × 602px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorcarpenterwilliambenja, bookcentury1800, bookdecade1840
