Quain's elements of anatomy . mitive blood and blood-vessels of the vascular area originate. The latter view is one which has long been advocated by various especially by His (No. 29 and No. 111. i. and ii.), who in 1868 described theorigin of the vascular as well as the connective tissues as taking place in the lowerlayer, and forming a special part of the mesoblastic elements under the name of2)arahlastic. Similar views as regards the origin of the blood and vessels fromperipheral blastodermic elements were brought forward by Peremeschko andmaintained by Strieker and other
Quain's elements of anatomy . mitive blood and blood-vessels of the vascular area originate. The latter view is one which has long been advocated by various especially by His (No. 29 and No. 111. i. and ii.), who in 1868 described theorigin of the vascular as well as the connective tissues as taking place in the lowerlayer, and forming a special part of the mesoblastic elements under the name of2)arahlastic. Similar views as regards the origin of the blood and vessels fromperipheral blastodermic elements were brought forward by Peremeschko andmaintained by Strieker and others of the Vienna school (Nos. 91 and 93). In mammals the vesicular form of blastoderm, which results from the OEIGIN OF THE LAYERS. 755 holoblastic segmentation of the ovum, seems to determine some modifi-cation in the mode of formation of the layers. As already stated, thecompletion of the primary segmentation leads to the covering in of thewhole ovum with a layer of flattened nucleated cells, within which. Fig. 645. Fk. Fig. 645.—Embryonic area from the ovum op a rabbit of seven days. Kolliker.) jpT, first rudiment of the primitive streak. Fig. 646.—Embryonic area from the ovum of a rabbit of eight days. \ Kolliker.) arg, border of the embryonic area ; pr, primitive streak with groove. f. (From (From besides the fluid remains of the original yolk-substance, there is theinner mass of granular cells or segmental spheres, which by their fmtherdevelopment and extension come to produce one or more deep or internallayers, which gradually spreading over the interior give a bilaminar ortrilaminar structure to an increasing area of the blastoderm. Fig. 647.
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