. Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals . FIG. 160.—Abnormal larval stages of the seaurchin, Sphcerechinus granularis, producedby heat. (After Driesch.) 280 EVOLUTION AND ANIMAL LIFE. FIG. 161.—A, Lateral view of pluteus larva ofEchinus; B, lateral view of pluteus larva ofSphiprechinus; C, hybrid pluteus of the femaleSphcerechinus and male Echinus. (After Boveri.) separated blastomeres of the two, four, eight, and even sixteen- cell stages of developing hydro-medusa eggs. Loeb was able to effect
. Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals . FIG. 160.—Abnormal larval stages of the seaurchin, Sphcerechinus granularis, producedby heat. (After Driesch.) 280 EVOLUTION AND ANIMAL LIFE. FIG. 161.—A, Lateral view of pluteus larva ofEchinus; B, lateral view of pluteus larva ofSphiprechinus; C, hybrid pluteus of the femaleSphcerechinus and male Echinus. (After Boveri.) separated blastomeres of the two, four, eight, and even sixteen- cell stages of developing hydro-medusa eggs. Loeb was able to effect the bursting of n /1\ & ^ ^ the membrane of sea- urchin eggs and the con-sequent partial escapeor protrusion of parts ofthe egg plasm formingso - called extra - of these extra-ovates began develop-ment as a distinct bias-tula, the remainder ofthe egg forming anotherblastula (Fig. 163).Thus we see that experimental work has, so far, not afforded a positive answer to the general query proposed by the pre- formation versus epigen- esis problem. But at the same time it is obvious that the results of the experimental method are of extraor-dinary interest and of brilliant promise. What seems to be revealed so far, is that the animal egg is certainly not rigidly
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