DEVELOPMENT OF THE BATH SPOXGE. 



317 



body by surrounding lacunar spaces. This seems to be an approximation to a rudimentary ovary. 

 The eggs come to maturity at all times of the year. The spermatozoa (Fig. 7) occur in globular 

 clusters, known as sperm-balls, each the product of a single cell ; they are strewn through the Sponge 

 and not collected in special areas. 



Ova and spermatozoa are never developed, or at all events have not been observed, in the same 

 individual, so that in the Bath Sponge, as in some other Sponges, though by no means in all, the sexes 

 are distinct. 



Development. The entrance of the spermatozoon into the ovum, which constitutes the essential 

 act of fertilisation, lias not yet been certainly observed in this or any other known Sponge, but the 

 resulting changes have been seen and carefully traced up to a certain stage. The ovum first divides 

 into two similar cells, each of these again subdivides, and four similar cells result ; subdivision again 

 takes place and eight cells result, and this process of segmentation is continued till at length a spherical 

 cluster of similar cells, the well-known mulberry- mass, or morula, is formed (Fig. 1). The morula 

 then becomes differentiated into an inner mass of connective tissue cells, and an outer layer of small 

 cylindrical cells, coloured by pigment granules, and each furnished with a flagellum. The flagellated 

 embryo extricates itself from the parent Sponge, and whirls rapidly about in the surrounding water. 

 It has a compressed oval form, and resembles the 

 planula of some corals. Its further history is unknown. 



Besides this natural mode of propagation the Bath 

 Sponge can be multiplied, like a plant, by artificial 

 cuttings. The demand in the arts for the Bath Sponge 

 being in excess of the supply, attention has been 

 directed to its cultivation, and with great success. The 

 Sponge is cut into pieces, about one inch cube, care 

 being taken to preserve as much of the skin and to 

 squeeze out as little of the flesh as possible ; the cut- 

 tings are then skewered on a strip of cane, and fastened 

 into a wooden frame, constructed to preserve them 

 from the access of mud and excess of light ; they are 

 then sunk in the sea at a depth of about five to seven 

 yards. In about seven years' time a crop of fine regularly globular Sponges is ready for the market. 

 A capitalist or a company is now all that is required to make Sponge farming a profitable 

 pursuit. 



Classification. The species of Sponge in common use are three : Euspongia officinalis (Lin.), the 

 fine Turkey or Levant Sponge, just described; Euspongia zimocca (Schmidt), the hai'd Zimocca 

 Sponge ; and Hippospongia eqnina (Schmidt), the Horse Sponge, or common Bath Sponge. The genus 

 Eusponyia is distinguished by the regular development of the skeletal network throughout the body, 

 its narrow meshes, scarcely or not at all visible to the naked eye, and the regularly radiate arrange- 

 ment of its chief fibres ; Hippospongia is distinguished by the thinness of its fibres and the labyrinthic 

 character of the skeleton beneath the skin, due to its being closely traversed by numerous winding 

 canals of about one-fifth to two-fifths of an inch in width. As a consequence its chief fibres have no 

 regular 1'adiate arrangement. 



The species of Euspongia are distinguished as follows : In E. officinalis the chief fibres are of 

 different thicknesses, irregularly swollen at intervals, and without exception cored by sand-grains ; in 

 E. zimocca the chief fibres are thinner, more regular, and almost free from sand ; in E. officinalis again 

 the uniting fibres are soft, thin, and elastic ; in E. zimocca denser and thicker it is to this difference 

 that the latter Sponge owes its characteristic hardness. Finally, the colour of the skeleton in E. offici- 

 nalis is a light clear yellow, in E. zimocca a dark brown yellow. The common Bath Sponge 

 (H. equina) has almost always a thick cake-like form, but its specific characters are not yet further 

 defined. 



Distribution. Euspongia officinalis is found at various parts of the Mediterranean coast, as also 

 are the other two species of Bath Sponge. A species not to be distinguished from it occurs also 

 in the Caribbean Sea about the shores of the West Indian Islands, and associated with it are two 



Fig. 7. SPERMATOZOA (ffalisorca Zobittoris). [After 



Schulze.] 

 A, Separate sijennatozoa, x 800 ; B, sperm ball, x 500. 



