J50 OPINIONS AND DISCOVERIES 



crept into their pores and holes for shelter, or for the pur- 

 pose of feeding on the sponge. The statement of this shrink- 

 ing under the divers' hand he considers to be equally in- 

 credible, but naturally enough explains the origin of the 

 story from what we know of the inherent elasticity of the 

 productions in question. He agi'ees wdth Tmperato in con- 

 sidering them as of all marine vegetables the most nearly 

 related to the Fungi, being composed of a substance like 

 compacted wool, perforated with tubes and holes, and cover- 

 ed over with a certain membranaceous mucilage. The 

 sponges li^'e affixed by a root to rocks, shells, and in sand ; 

 if torn away they shoot up again from their root and grow 

 as other plants do. Their peculiar property is to be easi- 

 ly compressed and then again to swell out to their pristine 

 bulk ; hence the facility with which they imbibe any fluid 

 and allow it to flow out on the application of convenient 

 pressure.* 



Even 30 late as the }ear 1760, when his views had been 

 well considered, Linnaeus arranged the " Spongia" amongst 

 the cryptogamous algae ;t but undoubtedly previous to this, 

 the position of the genus in the " Systema Naturae" had 

 been rendered vacillant by nqw discoveries. About the 

 commencement of the 18 th centiu'y, Marsigli, " that fair 

 investigator of nature," asserted that he had seen a motion 

 of contraction and dilatation in the pores or oscula of se- 

 veral sponges just removed from the sea-l Marsigli, how- 



Histoda Plantarutn, auct. Joanne Raio, i. p. 80; and iii. p. \6. 

 Lond. 1686. Syn. Stirp. Brit. i. p. 29. 



•t" Systema Naturae, edit. 10, ii. p. 1348. 



I " Plusieurs especes d'Eponges lorsqu'elles sortent de la mer ont 

 dans de certains petits trous un mouvemeiit de systole et de diastole, qui 

 dure jusqu'a ce que I'eau qu'elles renferment soit entierement consu- 

 niee." Hist, de I'Acad. Roy. des Sciences, 1710, p. 96. 



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