The philosophy of biology . on one part of the- . J hollow ball of cells be- comes pushed mwards, <Meso^^ ^^d the CcUs of this intumed layer become %-Endod^rm ^^^^^^^ ^^^^ ^^OSe of the external layer, while FIG. . sea-urchin Gastrula ^^1^^ \ ^ ^^^ ^in^ larva in section. appear in the space be- tween the external andinternal layers. This is the process of differentiationleading to the development of the various tissues—protective, sensory, digestive, skeletal, etc. The cellsstill continue to divide and grow to their maximalsize, but when the process of differentiation begins,the c
The philosophy of biology . on one part of the- . J hollow ball of cells be- comes pushed mwards, <Meso^^ ^^d the CcUs of this intumed layer become %-Endod^rm ^^^^^^^ ^^^^ ^^OSe of the external layer, while FIG. . sea-urchin Gastrula ^^1^^ \ ^ ^^^ ^in^ larva in section. appear in the space be- tween the external andinternal layers. This is the process of differentiationleading to the development of the various tissues—protective, sensory, digestive, skeletal, etc. The cellsstill continue to divide and grow to their maximalsize, but when the process of differentiation begins,the cells which are formed are not quite the sameas those from which they originated. Finally, how-ever, when the rudiments of aU the tissues of theadult body have been laid down, the ceUs begin toproduce daughter-cells of only one kind. Growth ofthe embryo consists, therefore, of the dissociation ordivision of the substance of the ovum and blastomeres,followed by a gradually increasing differentiation ofthe cells so THE INDIVIDUAL AND THE SPECIES 171 Reintegration proceeds all the time. Blastulaand gastnila larvae are really organisms capable ofleading an independent existence—that is, they areautonomous entities or individuals. The activitiesof the parts of which they are composed—ectodermallocomotory cells, ectodermal sensory cells, endodermalassimilatory cells, and so on, must be cells are in organic material continuity witheach other, and events which occur in any one of themaffect all the rest. Impressions made upon thesensory cells are transmitted to the locomotory cells,and food-material assimilated by the assimilatorycells is distributed to aU the others. At all stages thegrowing embryo is an organic unity. The more fullyit is developed, the greater the morphological com-plexity of the organism, and the more numerous itsactivities, the greater is the differentiation; but thegreater also is the co-ordination of the organs andtissues. In the
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjectbiology
