SPONGES 



If we examine a very simple sponge, such as 

 Ascetta, we see a small fMB-wapM body, fixed at 

 it~ base, open ill the ap-'\. 

 ExaillilK'il microscopical K 

 tills MUSI- shows mi internal 

 layer of ciliated cells, a 

 very delicate external skin, 

 antl between these a iniiUlle 

 stratum in which lie 

 numerous needles of lime, 

 which form the supporting 

 skeleton of the sponge. 

 Through the walls run 

 numerous fine canals, and 

 if we observe a larger 

 sponge living in water with 

 which a little powdered 

 carmine has been mixed 

 we can verify Grant's ob- 

 Fig. 1. Section through sedation that water passes 

 wall of Sycilla rhruta- ' m '>>' minute pores all over 

 if. showing various the surface and passes out 

 kinds of spicules, and by the larger apical aper- 

 pores in the wall. lures. On these currents 



of water, which continually 



feed and refresh the body, the life of the sponge de- 

 pends. Every Metazoon organism is ' a city of cells ' 

 ~-a sponge is peculiarly Venice-like. The currents 



Fig. 2. Section of part of a Sponge, Oicarella lobularii 

 (after Schnlze ), Knowing afferent canals, ciliated cham- 

 bers, efferent canals, internal cavities (e, e), segment- 

 ing ova (a, b, c, rf). 



are sustained by the activity of the internal ciliated 

 cells, which by their ceaseless lashing draw the water 

 inwards and drive it also outwards, and at the same 

 time absorb food- 

 particles which drift 

 along iii the current. 



But few sponges are 

 s<> simple as the vase- 

 like Ascetta ; we are 

 familiar, for instance, 

 with the complex 

 'horny' skeleton of 

 the bath -sponge (En- 

 spongia), or with 

 Kg. 3. Figure of Leucandra the beautiful flinty 

 aecharata, showing mode of framework of the 

 growth by budding. Venus' Flower-basket 



( Euplectella) ; and an 



examination of the fresh-water simnge (S|>ongilla) 

 of the lake or canal, or of the Mermaids' Gloves 

 (Chalina) HO often ca*t up half alive on the beach, 

 convinces us that the structure of the soft part* is 



also relatively < plex. Yet with the simple primi- 

 tive oups, the most complex forms are connected l>v 

 a gradual series of steps, and simple cups they all 

 are when very young. Let us consider hi icily how 

 the complication of structure is brought about. 



( 1 ) The vegetative character of s]>onge.s is shown 

 by the prolific way in which buds grow out fnun 

 the parent body. These buds may produce other 

 buds, and the walls of neighbour-buds may fuse ; 

 in this way there arise from an original sac-like 

 form complex structures puzzling to those who 

 seek logical clearness a* to the nature of animal 

 individuality (see fig. 3). 



1 - i In the simple .Won type the internal cavity 

 is lined by the characteristic Monad-like, 'col- 

 lared,' ciliated cells. If this layer grow more 

 rapidly than the outer strata it will naturally 

 become folded into a number of side aisles, anil 

 this is seen in the Syeon type of calcareous spin 

 in which the characteristic collaret! ami ciliated 

 cells are restricted to a series of radial cliiiinliers 

 around the central cavity. If a similar process 

 of folding occur in the radial rhaml>ers the char- 

 acteristic collared and ciliated cells become restricted 

 to little ciliated ampulla- or clmml>ers, which affer- 

 ent canals from the surface enter, and from which 

 efferent canals lead to the central cavity ami thence 

 outwards. This is the state of affairs in the 

 Lencon type of calcareous sponges, and, with further 

 complications, in the great majority of forms. 



(3) Another seat of complication j_ the middle 

 stratum. This is called the mesogltca in order to 

 emphasise the fact that in sponges, as also in 

 ( 'o'lenterates, it has not the same definiteness as 

 the middle layer or mesodeim which occurs in the 

 Ccelomata, that is, in all animals higher than 

 Coelenterata. In the simple sponges the middle 

 stratum is very simple, and always it seems to owe 

 its units to contributions from the inner layer or 

 endoderm. In more complex forms, however, the 

 me.sogluea contains a great variety of cells : some 

 skeleton-making, others contractile, others like 

 simple connective tissue, others full of pigment, 

 others forming reproductive elements, and so on. 

 In sponges the outer layer or ectoderm is always 

 unimportant, though it may line the outer portions 

 of the inhalent canals ; the mesoderni forms the 

 skeleton and contains the reproductive elements ; 

 the inner layer or endoderm is very important, 

 including, as it does, the collared ciliated cells 

 which cause the water-currents am! absorb the 

 food, as well as other flattened and often ciliated 

 cells which line the efferent channels. 



Life of S]mges. Although sponges do not move, 

 there is great motor activity in the ciliated cells of 

 the endoderm. Like many othei -passive organisms 

 sponges are profoundly influenced by their surround- 

 ings, for their shapes vary according to the nature 

 of their anchorage and the currents which play 

 around them. Sensitiveness to stimulus ! slmn 

 by the closure of the little superficial pores and 

 sometimes even of the larger exhalent aperture or 

 apertures. This closure is due to special con- 

 tractile-cells in the mesogloea, and in some cases it 

 seems that these are connected with sensitive and 

 nervous cells on the surface. The food of sponges 

 consists of microscopic organisms and particles of 

 organic debris, which are borne by the water- 

 currents, and caught by the ciliated cells which, 

 like so many Monads, swallow first and ili 

 intracellularly afterwards. From the cells which 

 feed surplus nutritive material oozes to adjacent. 

 cells, or is passed to mobile amcalioid cells in the 

 niesoghra. Useless debris is also got rid of by the 

 collared cells. Respiration is of course effected by 

 the currents of water which wash the cells, and 

 some of the bright pigments, such as floridine, 

 characteristic ot many sponges, readily absorb 



