The doctrine of descent and Darwinism . d. All further developmentemanates from these primordial seg-ments, which are the standard of theAnnelids or higher Vermes ; while inthe Articulata, projections and ap-pendages of these segments developinto feelers, manducatory apparatusand legs, and by their heterogeneousintegration in the regions of thehead, and of the middle and posteriorportions of the body, give rise to thevast variety within the type. In eachparticular case we see what is specialemanate from what is more homogeneous and undiffer-entiated, and this is likewise corroborated by the mo
The doctrine of descent and Darwinism . d. All further developmentemanates from these primordial seg-ments, which are the standard of theAnnelids or higher Vermes ; while inthe Articulata, projections and ap-pendages of these segments developinto feelers, manducatory apparatusand legs, and by their heterogeneousintegration in the regions of thehead, and of the middle and posteriorportions of the body, give rise to thevast variety within the type. In eachparticular case we see what is specialemanate from what is more homogeneous and undiffer-entiated, and this is likewise corroborated by the moreadvanced phase portrayed in the diagram (fig. 6). Itrepresents the embryo of the great black-beetle (Hydro-philus piceus) on its ventral side. The antennae (/), thethree pair of oral appendages (;;/), and the three pair oflegs, are as yet little distinguished. In the further courseof development, the lateral portions grow tow^ards theback, in the centre of w^hich they finally meet. Ascompared wath the Vertebrata, it may hence be said. 54 THE DOCTRINE OF DESCENT. that the Articulata have their navel on their , it is the characteristic of the evolutionary-type of the Vertebrata that the position of the germcorresponds with the dorsal side of the animal. Theformation of the dorsal groove, which subsequentlycloses to form the canal of the spinal cord, as it isgradually enveloped in a sheath growing from below,is followed by the formation of transverse plates, thepre-vertebral plates. The side plates lying outside ofthese grow towards the ventral side, and finally mergein the navel. The position of the actual vertebralcolumn, consisting of separate vertebrae, is alwaysoriginally occupied by a cartilaginous band, the noto-chord (chorda dorsalis), and, as from this axis, the germi-nal matter transforms itself into a tube above as well asbelow,—into the spinal marrow with its sheath, and theventral cavity with the intestinal canal,—Von Baer con-sidered this mode o
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Keywords: ., bookauthorschmidtd, bookcentury1800, bookdecade1880, bookyear1882
