The Journal of experimental zoology . vertex lies at or near the old median exis,and the angle at the vertex is 90° or less, the cut edges are equalin length, then the piece regenerates a head which is at rightangles to the original median axis (figs. 5 to 10); if a pharynxdevelops, which very rarely happens (two cases only), this organappears between the eyes and points toward the tip of the newhead (fig. 7e, 9). The number of cases illustrating Group D was,in Series I, 15, in Series II, 5. In the regeneration of all othertypes of triangular pieces, the size of the piece influences the 164 J.


The Journal of experimental zoology . vertex lies at or near the old median exis,and the angle at the vertex is 90° or less, the cut edges are equalin length, then the piece regenerates a head which is at rightangles to the original median axis (figs. 5 to 10); if a pharynxdevelops, which very rarely happens (two cases only), this organappears between the eyes and points toward the tip of the newhead (fig. 7e, 9). The number of cases illustrating Group D was,in Series I, 15, in Series II, 5. In the regeneration of all othertypes of triangular pieces, the size of the piece influences the 164 J. M. D. OLMSTED final regenerated form, but several specimens which fulfilled theconditions of Group D and had heads at right angles to the oldmedian axis were larger th-an those which did not fulfill theseconditions and retained their old polarity. Such a regenerated worm lives for days or even weeks withoutchange, except a diminution in size, until it disintegrates. Itrareh moves about in its dish, but when disturbed it moves rap-. Fig. 6 Case similar to that of figure 5; a, showing region from which the piecewas taken; b, 3 days after operation; c, 5 days; d, 7 days; e, 14 days. idly in the direction in which the head points, or in wide curveswith the original posterior edge directed toward the center ofrevolution. During the first two or three days of the regeneration of thesetriangular pieces whose heads develop at right angles to the oldlong axis, accumulation of new material occurs along both anteriorand posterior edges, but the amount along the anterior edge isusually the greater (figs. 5d, 6c, 7b). Morgan (98), in speak-ing of the regeneration of right-angled triangular pieces, says, A STUDY IN POLARITY 165 Although the amount of old tissue at the anterior end is rel-atively little, yet the growth of the new material that forms inthis region is greater than that of the material at the side im-mediately behind the head and along the side of the piece. Morematerial is fo


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Keywords: ., bookauthorwi, bookcentury1900, bookdecade1910, booksubjectzoology