SPONGES 



653 



oxygen. The green pigment of Spongilla is at 

 least closely analogous to chlorophyll. 



Reproduction. Sponges multiply, like many 

 plants, by overgrowth and budding, but the buds 

 remain continuous with the parent mass, though 

 sometimes it happens that small portions are set 

 adrift from a moribund body. As a sponge is but 

 slightly differentiated, as a fragment is a fair 

 sample of the whole body, we can understand the 

 success with which the sponge-farmers bed out 

 portions of sponge in suitable places, leaving them 

 to grow to a size fit for use. But sexual reproduc- 

 tion also occurs in all sponges. The ova and sper- 

 matozoa are included in the mesoglrea, originating 

 from apparently similar cells. Both unisexual and 

 bisexual forms occur, in rare cases within one 

 species. The. ova are fertilised by spermatozoa 

 drawn in by the water-currents, and development 

 proceeds through several stages before the embryo 

 leaves the parent (see fig. 2). 



The life-history of the fresh-water sponge, Spon- 

 gilla, as told by Marshall, is one of interesting 

 vicissitudes. In autumn the sponge begins to suffer 

 from the cold and the scarcity of food, and dies 

 away. But throughout the moribund parent clumps 

 of cells combine into 'gemmules,' which are fur- 

 nished with capstan-like spicules, and are able to 

 survive the winter. In April or May they float 

 away from the parental corpse, and form new 

 sponges. Some of these are short-lived males, 

 others are more stable females. The ova pro- 

 duced by the latter, and fertilised by the cells 

 of the former, develop into another generation of 

 sponges, which in turn die awav in autumn, and 

 give rise to gemmules. The life-liistory thus illus- 

 trates Alternation of Generations (q.v. ). 



Development. The development of sponges varies 

 considerably in the different types, but we may 

 sketch that of a calcare- 

 ous sponge. The fertilised 

 ovum divides completely, 

 and forms a hollow sphere 

 of in part ciliated cells, 

 which escapes from the 

 parent into the water. In 

 the course of a short free- 

 swimming life the ball of 

 cells becomes invaginated, 

 and forms a two-layered 

 gastrula. This fixes itself, 

 mouth downwards. But 

 pores soon appear through 

 the walls ; the internal 

 cells which had meanwhile 

 lost their cilia regain them : 

 an exhalent orifice is formed 

 by rupture at the apex ; a 

 middle stratum is derived 

 from the inner layer and 



Fig. 4. Two stages in 

 the development of 

 Nnffindra raphania 



(after Sch ulzf)-: 

 a, gutrula, toward! end 

 of free-swimming stage ; 



lection of embryo after logins to form spicilles : the 

 " 



layers and the central assication. One of 



cavity. the oldest and most con- 



venient classifications of 



sponges is that which distinguishes three main sets 

 according to the nature of the skeleton : 



(1) CALCISPOXOI.* : with spicules of carbonate of lime, includ- 

 ing Aacon, Sycon, and I-eucon types. The purse-like 

 Sycandra (or trrantia) compresta la common on British shores. 



(1) 8lLlcl8POxoi/e : with piculen and threads of silica e.g. 

 the Venus' Fluwcr-basket (Euplectella); the likewise deep- 

 tea Glass-rope Sponge (Hyalonema); Mermaids' Gloves 

 (Chalina oculatn , with a fibrous as well as a flinty skeleton ; 

 the common Crumb-of-bread Sponge (tialichondria panicta ; 

 Clione, which bores in oyster shells; Subtrites domnncula, 

 which grown round a whelk shell inhabited by a hermit-crab ; 

 and the fresh-water Hpongilla. 



(8) CKRATOWOKOI.* : with a framework of spongln or sponge- 

 stuff and no proper spicules e.g. the Bath-sponge (Bu- 

 spongia), which thrives on some of the Mediterranean coasts. 



To these may be added a few, probably degene- 

 rate, forms which have no skeleton at all (Myxo- 

 spongije) e.g. Oscarella ( or Halisarca ) lobularis. 



History. Sponges, as we should expect, occur in 

 very ancient strata ; remains of a flinty form ( Proto- 

 spongia) have been found in Cambrian strata. 

 In succeeding ayes they are almost always repre- 

 sented. Remains of calcareous forms are almost 

 confined to one peculiar set of large forms (Phare- 

 trones) in Devonian and several succeeding 

 epochs. Professor Franz Eilhard Schulze the 

 greatest authority on sponges divides the sponge 

 branch of the genealogical tree into three : the 

 calcareous forms to one side, the siliceous Hex- 

 actinellida with triaxial spicules to the other, and 

 between these the other flinty sponges whose 

 spicules have four axes (Tetraxonia) or only one 

 (Monaxonia), and the horny sponges without any 

 spicules. It is generally allowed that the sponges 

 are quite distinct from the Crelenterates, and that 

 they are somewhat degenerate and divergent 

 descendants of the primitive Metazoa. 



Relation toother Organisms. ' Sponges are living 

 thickets in which many small animals play hide- 

 and-seek.' Polypes, worms, and some other 

 animals are often found associated with sponges, 

 using them partly for shelter, partly as browsing- 

 grounds. From the appetite of larger animals 

 sponges are doubtless in great part saved by their 

 spicines, and their frequently offensive taste and 

 odour. Some sponges are borers, and others 

 smother forms of life as passive as themselves. 

 Several crabs are masked by. growths of sponge, 

 and within several sponges minute Algse live in 

 constant partnership. 



Several species of Euspongia are in use for econ- 

 omic purposes. Two species are brought from 

 the Levant, and one (not much inferior) from the 

 West Indies and coast of Florida. The trade in 

 sponge is very considerable ; it is carried on chiefly 

 by Greeks, Sicilians, and Tunisians, and by the 

 inhabitants of the Bahama Islands. The num- 

 lier of men employed in the Levantine sponge- 

 fishery is l>etween 4000 and 5000, forming the 

 crews of about 600 boats. These boats find their 

 chief employment on the coasts of Candia, Bar- 

 bary, and Syria. The sponge is obtained by 

 diving, the diver taking down with him a flat piece 

 of stone of a triangular shape, with a hole drilled 

 through one of its corners ; to this a cord from the 

 boat is attached, and the diver makes it serve to 

 guide him to particular spots. When he reaches 

 the growing sponges he tears them off the rocks, 

 and places them under his arms ; he then pulls at 

 the rope, which gives the signal to his companions 

 in the boat to haul him up. The value of sponges 

 collected in Greece and Turkey is from 90,000 to 

 100,000 annually. The diving-bell and diving- 

 dress are sometimes made use of. The Greeks of 

 the Morea, instead of diving, obtain sponges by a 

 pronged instrument ; but the sponges thus collected 

 are torn, and sell at a low price. The best sponges 

 are obtained on detached heads of rock in eight or 

 ten fathoms water. 



The sponges of the Bahamas and other West 

 Indian islands are of a larger size and coarser 

 quality ; the sponge-trade there employs 500 small 

 vessels and 5000 to 6000 people ; in 1890 the crop 

 exceeded 900,000 lb., worth 61,400; and about 

 215,000 lb., worth 17,000, are sent annually to 

 Great Britain. The sponges are torn from the 

 rooks by a fork at the end of a long pole. To get 

 rid of the animal matter they are buried for some 

 days in the sand, and then soaked and washed. 



The domestic uses of sponge are familar to every 

 one. It is also of great value to the surgeon, not 

 only for removing blood in operations, but for 

 checking haemorrhage. Burnt sponge was once a 



