Echinoderm Larvce ivith Two Water-Vascular Systems. 345 



the right coelomic wall, so that they are able under the influenoe of a 

 hydrocQsle bud to give rise to structures to which in the history of the race 

 they have never given rise. It is well to remind ourselves that this amazing 

 phenomenon does not stand alone. The facts that when the eye-stalk of a 

 shrimp, including the underlying optical ganglion, is cut out, the stump 

 regenerates not an eye but an antenna, and that further when the primary 

 optic vesicle of a young tadpole is cut off from the brain and pushed 

 backwards under the skin into the region of -the shoulder it will force the 

 local ectoderm to form for it a lens, warn us that living developing tissues 

 do not obey the laws with which we become familiar when we study dead 

 matter. 



In many cases, at any rate, the body of an embryo is not, like a picture 

 puzzle, a mosaic of pieces each destined to form a- particular organ, but 

 consists of sheets of indifferent material " without form and void " on which 

 a formative " something " works and evokes the beautiful detail of the adult 

 structure. As Driesch (3) has expressed it, " Ein jedes jedes kann." 



BIBLIOGRAPHY. 



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(4) Driesch, H., ' Analytische Theorie der organischen Entwicklung,' Leipzig, 1894. 



(5) Gemmill, J. F., " The Development and Certain Points in the Adult Structure of 



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(9) Grave, Caswell, "Notes on the Metamerism of the Echinoid Pluteus," 'Johns 



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(10) Loeb, J., 'On the Artificial Production of Normal Larvse from the Unfertilised 



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(12) MacBride, E. W., " The Development of Echinoids. Part I.— The Larvae of Echinus 



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(13) MacBride, E. "W., "The Development of Echinus esculentus, together with Some 



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(14) MacBride, E. W., " Two Abnormal Plutei of Echinus and the Light which they 



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