July 1. 1899. 



KNOWLEDGE 



■145 



^ iJ.lTERATURE¥ 



Founded by RICHARD A. PROCTOR. 



LONDON: JULY 1, 1S99. 



CONTENTS. 



Sponges and the Sponge Trade. By E. Ltdekksr. 



(Illustrated) 



The Energy of Rontgen Rays. By Dr. J. G. McPhesson, 



F.R.8.E. ... 



The Story of the Orchids.— I. By the Kev. Alex. S. 



Wilson, M. A , B.sc. (Illustrated) ... ... 



Microbes in Cooperation. By &. Claekb Nuttall, b.sc. 

 Distribution of Stars in Space. By Gatin J. Buens, b.sc. 



(Diaflrams) ... ... ■■ ■-. ■■_■ _ ■■■ 



The Zodiacal Coins of the Emperor Jahangir. By E. 



Walter Mauxdee, f.e.a.s. (Plate) 



Galileo's Tower at Florence. By W. Alpeed Parr. 



(Illustrated) " 



Science Notes .. 



British Ornithological Notes. Conducted by Haeet F. 



WiTHBEBT, F.Z.8., M.B.O.U 



Notices of Books 



Books Received 



The Mycetozoa, and some Questions which they 



Suggest. — IV. By the Eight Hon. Sir Edwabd Frt, 



D.C.L., LL.D., F.R.S., and AGNE3 Fet. (Illustrated) 

 Electricity as an Exact Science. — IV. Experience, its 



Value and its Danger. By IIowabd B. Little 

 The Teeth on the Labella of the Blow Fly. By Walter 



WesCbe. (Illustrated) 



Microscopy. By John H. Cooke, f.l.s., f.g.s. 



Notes on Comets and Meteors. By W. F. DEXuiNa, 



r.E.A.8 



The Face of the Sky for July. By A. Fowleb, f.e.a.s. 

 Chess Column. By C. D. Locock, b.a. 



apertures appear and disappear at intervals. If cut, the 

 interior presents somewhat the appearance of raw meat, 

 intersected by numerous canals and cavities. These latter 

 are lined with a sticky, greyish-brown substance, termed 

 "milk" by the sponge-gatherers, and sarcode by anatomists. 

 In a sponge of simple structure, such as one of the 

 " fingers " of the glove-sponge (Fig. 1), the water is drawn 



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SPONGES AND THE SPONGE TRADE. 



By E. Lydekkee. 



THE ordinary conception of sponges being derived 

 from the horny skeletons of the various kinds 

 employed for domestic purposes, it is by no means 

 generally realised that the graceful object known 

 as Venus's flower-basket is the skeleton of another 

 member of the same group ; neither is it by any means a 

 matter of common knowledge that sponges really belong 

 to the animal kingdom. Indeed, it is not many years ago 

 that Messrs. Cress well Brothers and Schmitz, the great 

 firm of sponge-importers in Ked Lion Square, received an 

 official letter in which they were addressed as sponge 

 manxifacturers. 



Much of the ignorance connected with sponges is doubt- 

 less attributable to our acquaintance with these organisms 

 being generally limited to the skeleton, or framework, 

 whether this be horny, as in the case of the toilet-sponge, 

 or flinty, as in the Venus's flower-basket. Were the 

 sponge, as brought up fresh from the sea-bed, a familiar 

 object, little, if any doubt would be entertained as to its 

 animal nature. 



As it comes up from the sea, an ordinary sponge is a 

 fleshy-looking substance covered with a firm skin, in which 



Fig. 1.— Fine G-love-Spoiiiiie. Spongia officinalis tulv.Ufera. 

 West Indies. 



from the exterior through a number of pores in the surface 

 of the sarcode, and after passing through the canals and 

 chambers of the interior of the sponge-substance, is finally 

 discharged by the oscula, or " waste-pipes," at the summits 

 of the "fingers." In its course from the pores to the 

 mouths the water passes through minute sacs, or chambers, 

 lined with ciliated cells ; and it is the currents induced 

 by the waving of the fine hairs borne by the ciliated cells 

 that keep up the circulation of water, and thus bring a 

 continuous supply of food to the organism. As regards 

 the reproduction of sponges, it will suffice to say that this 

 ia generally carried on by a true sexual process ; the 

 fertilised germs being carried out by the waste-pipes, and 

 settling upon some neighbouring rock, pebble, or other 

 object, where it commences to grow. Concerning the 

 rate of growth of sponges, it may be mentioned that an 

 ordinary bath-sponge measuring about a foot in diameter 

 is approximately ten years old. 



Commercial sponges, forming the family Spongiida, are 

 the typical representatives of the entire group, and belong 

 to a section in which the skeleton is composed of a horny 

 substance, nearly related in structure to silk, and tech- 

 nically known as spongin. In many members of the 

 section this spongin is hard and brittle, and it is only 

 those kinds in which it takes the form of a soft elastic 

 network that are of any commercial value. 



The first thing to be done after a commercial sponge 



