[220] The recent researches of Selenka, Zeitschrift f. Wiss. Zoologie, Vol. XXVII. 1876, demonstrate that in Echinoderms the muscles are derived from the cells first split off from the hypoblast, and that the diverticula only form the water-vascular system and the epithelial lining of the body-cavity.
[221] Kowalevsky, “Würmer u. Arthropoden,” Mém. Acad. Pétersbourg, 1871.
[222] “Zur Entwicklungsgeschichte d. Brachiopoden”, Protokoll d. ersten Session der Versammlung Russischer Naturforscher in Kasan, 1873. Published in Kaiserliche Gesellschaft Moskau, 1874 (Russian). Abstracted in Hoffmann and Schwalbe, Jahresbericht f. 1873.
[223] Comparison of Early Stages, Quart. Jl. Micros. Science, July, 1875. [This Edition, No. VI.]
[224] “Urinogenital Organs of Vertebrates,” Journ. of Anat. and Phys. Vol. X. [This Edition, No. VII.]
[225] Entwicklungsgeschichte der Unke, Pl. 1, fig. 8.
[226] This membrane is better looked upon, as is done by Gegenbaur and Götte, as intercellular matter.
[227] The apparent structure in the sheath of the notochord in this and the succeeding figure is merely the result of an attempt on the part of the engraver to represent the dark colour of the sheath in the original figure.