. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. No. 6.] THE CESTODE MO \IEZIA EXPANSA. 271 face to form the anterior boundary of a, then making one more complete turn and ending on the upper surface, thus leaving b and c incompletely separated at the right of the dorsal surface. The development of the genital organs is sufficiently advanced in this case to show the very intimate relation of these organs as regards position with the form and relations of the proglot- tids. The segment a possesses its own genital mass (a1), which is entirely separated from all the others. T
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. No. 6.] THE CESTODE MO \IEZIA EXPANSA. 271 face to form the anterior boundary of a, then making one more complete turn and ending on the upper surface, thus leaving b and c incompletely separated at the right of the dorsal surface. The development of the genital organs is sufficiently advanced in this case to show the very intimate relation of these organs as regards position with the form and relations of the proglot- tids. The segment a possesses its own genital mass (a1), which is entirely separated from all the others. This is, however, of less than the normal size and does not reach the edge of the segment. It is divided into two parts in its inner portion, but the group of cells which would later form the ovary and vitel- larium does not appear. In fact, the mass seems to consist largely, if not wholly, of portions of the two ducts. It will be remembered that the ducts lie farther dorsally than do the ovary and vitellarium. The figure is drawn with the dorsal surface uppermost, and it is only dorsally that the region a appears as a distinct partial proglottid. On the ventral surface the relations of the furrows are entirely different. It appears then that the dorsal re- gion of a possesses a degree of individuality sufficient to cause the appearance of the organs proper to this region. The ven- tral region not being separated from b, the organs of the ventral side do not appear. Whether the organs would in later stages approach or reach the normal development it is impossible to state with certainty, but the evidence seems to be against such a view, for in all cases of similar abnormalities in much later stages the genital organs or parts, however rudimentary they may be, show the same degree of differentiation as those of normal segments. In the large, incompletely separated segments b and c, there appears another example of the close relation between the indi- viduality of the segment and
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
