. Text-book of embryology. Embryology. XV NEMATODA 447 the dorsal surface. These at first form two rows interdigitating with each other, but they quickly rearrange themselves so as to form a single row of band-like cells. Miiller has observed two large clear cells lying on the ventral surface in the anterior part of the animal. These he surmises to be the mother cells of the excretory tubes. Although these tubes extend in the adult through nearly the entire length of the animal, they are each composed of a single hoUowed- out gen. gen. Fig. 351.—Transverse sections of embryo of Ascaris
. Text-book of embryology. Embryology. XV NEMATODA 447 the dorsal surface. These at first form two rows interdigitating with each other, but they quickly rearrange themselves so as to form a single row of band-like cells. Miiller has observed two large clear cells lying on the ventral surface in the anterior part of the animal. These he surmises to be the mother cells of the excretory tubes. Although these tubes extend in the adult through nearly the entire length of the animal, they are each composed of a single hoUowed- out gen. gen. Fig. 351.—Transverse sections of embryo of Ascaris megalocephala, in order to show the invagination of the anterior mesoderm cells and of the mother cells of the genital organs. (After Boveri.) A, soction of a stage in which the endoderm cells are invaginated, but in which the mesoderm cells are still superficial. B, section of a stage in which the mesoderm cells have passed into the blasto- coelie cavity. C, section of a stage in which the genital cells are beginning to be invaginated. D, section of a stage in which the invagination of the genital cells is complete. When the young worm finally hatches out—which, under normal circumstances, must occur amongst the horse-dung which has been dropped on the ground — it is known as a Rhabditis larva, and it only becomes converted into a mature worm after it has been swallowed by a horse. The reader will not fail to observe what large gaps there are in the account of the development which has just been given, and what a field there is for future work. The problem of tracing the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
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Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
