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ON THE STRUCTURE AND LIFE-HISTORY OF SPONGES. 

 By R. von Lendenfeld, Ph.D., F.L.S. 



Sponges are exceedingly variable in shape. Their primordial 

 form is the same as that of the higher Coelenterates, the Gastrula. 

 The wall of the originally simple Gastrula-sac is folded con- 

 siderably in the higher sponges. Great quantities of mesodermal 

 ground- substance are produced and occupy these folds ; thus the 

 massive body of the sponge is formed. The gastral cavity becomee 

 the oscular tube which communicates with the surrounding water 

 by the oscula or vents. The terminal opening of large tubular 

 sponges is generally not an osculum, but a pseudosculum. In that 

 case the true oscula are situated in the inner wall of the tube. 



The sponges which are regular in shape are mostly radially 

 symmetrical, without distinct anti- or metameres. There are, 

 however, also forms known with a definite number of antimeres, 

 but these are rare. Only one bilaterally symmetrical sponge, a 

 tree-shaped Halichondrine {Esperiopsis challengeri, Kidley), has 

 been described hitherto. This consists of a slender cylindrical 

 stem, to the sides of which regular bilaterally symmetrical, 

 kidney -shaped fronds are attached by long peduncles. The 

 Hexactinellidce and Syconida are distinguished by their regular 

 radially symmetrical shape. These are sac-shaped. The Tethyidcs 

 are pretty regularly spherical. A great many of the Chondro- 

 spongice and most Cornacuspongm, particularly the Horny 

 Sponges, are quite irregular in shape. The distinctive features 

 of the species appear as combinations of peculiarities which are 

 very unimportant in themselves, but which combined characterise 

 the form and enable one to identify the sponges. 



The size of sponges is, like their shape, subject to great varia- 

 tion. The smallest sponges, excepting the doubtful Physemaria, 

 are the most simple forms of calcareous sponges, the Asconida. 

 The largest forms we find among the Chondrospongm and Coma- 

 cuspongice. There is in the British Museum a fragment of a 

 cylindrical Suffaria from the West Indies, which is nearly 

 1|- metres long and 20 cm. thick. The specimens of Euspongia 

 from the Bahamas, particularly the flat, cake-shaped forms, some- 

 times attain a breadth of 1 metre and a height of 25 cm. The 

 largest sponges known are the species of Poterion described by 



