. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 66 IN VERTEBRA TB MOHPUOLOG Y. The fact that in some cases both immigration and delamination may occur simultaneously, leading to the formation of a sterrula, bears out the idea that the latter process has arisen from the former. Furthermore, it may be pointed out that the occurrence of immigration in such colonial Flagellates as Votoox indicates the primitive character of immigration in the Metazoan blastulas, as well as the manner in which diploblastic organisms have
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 66 IN VERTEBRA TB MOHPUOLOG Y. The fact that in some cases both immigration and delamination may occur simultaneously, leading to the formation of a sterrula, bears out the idea that the latter process has arisen from the former. Furthermore, it may be pointed out that the occurrence of immigration in such colonial Flagellates as Votoox indicates the primitive character of immigration in the Metazoan blastulas, as well as the manner in which diploblastic organisms have arisen from the more primitive single-layered organisms. It is only in the lowest Metazoa, however, that the adult organism is diploblastic. In all others a triploblastic (Fig. dm sm spitt. bm vm. Fig. 27.—Diagrammatic Tuansverse Section of an Earthworm to snow TIIK TuiPLOltLASTIC CONDITION. bm = basement membrane. C = ca'loin. dm — mesentery. ec = ectoderm. en = endodenn. S7n = soiniitio mesoderm. spin = spliinchuic niesoi'frm xm = veutial meseuter}'. 27) condition supervenes during embryonic life, by the devel- opment of a third layer, primitively separated from the eudo- derm, and occupying the space which may remain between the two primitive layers. This is the secondary germ-layer or mesoderm. From it there arise the muscular, excretor}', circulatory, and reproductive systems in the triploblastic ani- mals, the first and last of these bein<r derived in diploblastic forms from either one or both of the iniiii ''v layers, while the excretory and circulator}' systei s a e not differentiated. The manner of formation of i ^'smlerm i the embryo varies greatly. In some cases it .. ses as bilateial pouch-like outgrowths of the archenteron, Avhicii la er form closed sacks completely surrounding the digestive tract, the sack of either. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colora
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
