. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 204 Mr. F. S. Conant on the Chcetognaths. out plainly in the living object at this stage is found in sections to be the stalk-cell, which thus precedes the ovum in its passage into the duct. The ovum itself now changes its spherical shape hj sending out a projection, bearing the stalk- cell, into the duct. Then by a progressive series of changes in shape, such as is represented in fig. 2, each ovum makes. OWD' 5 4. Diagrams illustrating the successive stnges of constriction in
. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 204 Mr. F. S. Conant on the Chcetognaths. out plainly in the living object at this stage is found in sections to be the stalk-cell, which thus precedes the ovum in its passage into the duct. The ovum itself now changes its spherical shape hj sending out a projection, bearing the stalk- cell, into the duct. Then by a progressive series of changes in shape, such as is represented in fig. 2, each ovum makes. OWD' 5 4. Diagrams illustrating the successive stnges of constriction in the passage of an egg into the oviduct. O, o\um; S, stalk-cell; IWU, inner wall of the oviduct; O WD, outer wall its way into the oviduct. It is evidently passing through some such interspace in the wall of the oviduct, as was supposed by Grassi. The process occupies about eight or ten minutes. All the ova of one side pass through the successive stages of constriction at essentially the same time, the anterior being slightly in advance of the posterior. There may be a difference of time, however, between the ova of the two sides. The eggs remain in the oviduct from twenty minutes to half an hour before being laid, during which time the layer of gelatinous substance that surrounds each is thickened. The chief change, however, is a gradual compression of the eggs from before backward, so that they become ellipsoidal. The process is aided by contractions of the ovary, especially observed at the anterior end, and as a result the eggs are pushed backward toward the external opening. When the pressure has become great enough to overcome the resistance, which seems to be offered largely by a kind of mucous plug in the orifice, the eggs are extruded as two linear rows, one from each oviduct, the whole comprising anywhere from a few to sixty or seventy Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - col
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