SPONGES 



51 



Family 1. TETEACLADID^ With the characters of the sub- 

 order. Examples : Theonella, Gray (fig. 21 ic) ; Discodcrmia, Bocage; 

 *Siphonia, Parkinson. 



Sub-order 2. RHABDOCREPIDA. 



The desmas are of various forms, produced by the growth of silica 

 over a uniaxial spicule. 



Family 1. HEGAMORINID.E. The desmas are comparatively 

 large. Triaenes, usually dichotriaenes, help to support the ecto- 

 some. Microscleres usually spirasters. Examples : Corallistes, 

 O.S.; *Hyalotragos, Zittel ; Lyidium, O.S.; * Dorydermia, Zittel. 



Family 2. MICKOMOKIXID.Z. The desmas are comparatively 

 small. Trisenes and microscleres are both absent. Examples : 

 Azorica, Crtr.; *Verruclina, Zittel. 



Sub-order 3. AXOJfOCLADIXA. 



Desmas with a massive nucleated centrum, from which a variable 

 number of arms (28) extend radiately (see fig. 12/). Examples : 

 Vctulina, O.S.; Astylospongia, Boemer. 



Reproduction and Embryology. 



Fresh individuals arise by asexual gemmation, both 

 external and internal, by fission, and by true sexual repro- 

 duction. 



Asexual Fission is probably one of the processes by which com- 

 multipli- pound sponges are produced from simple individuals. 

 catlon - Artificial fission has been practised with success in the 

 cultivation of commercial sponges for the market. Ex- 

 ternal gemmation has been observed in Thenea, Tethya, 

 Pol ymastia, and Oscarella. A mass of indifferent sponge- 

 cells accumulates at some point beneath the skin, bulges 

 out, drops off, and gives rise to a new individuaL Internal 

 gemmation, which results in the formation of a statoblast, 

 is only known to occur in the freshwater Spongillidz. 

 The statoblasts consist of a mass of yolk -bearing 

 mesoderm cells, invested by a capsule, which in 

 Ephydatia fluviatilis is composed of an inner 

 cuticle of spongin separated from a similar outer 

 layer by an intermediate zone of amphidisks and 

 interspersed protoplasmic cells. On one side of 

 the capsule is a hilum which leads into the interior. 

 Their development has recently been studied by Gotte, 

 with results that confirm the conclusions of Carter (j) 

 and Lieberkiihn (/j). The process commences with an 

 accumulation of amoeboid cells within the mesodenn to 

 form a globular cluster ; yolk granules develop within 

 them, especially in those that lie nearer the centre. The 

 external cells give rise to the investing capsule ; some 

 resemble sponginblasts and secrete the inner and outer 

 horny cuticle ; others give rise to the amphidisks and 

 interspersed cells of the middle layer. Under favourable 

 conditions the interior cells creep out through the pore 

 of the capsule, and form a spreading heap, which by 

 subsequent differentiation gives rise to a young Sponyilla. 

 Since the freshwater sponges can only be regarded as 

 modified descendants of ancient marine species (prob- 

 ably of the family Halichondridx), we may consider the 

 internal gemmules, like the similar statoblasts of the 

 freshwater Polyzoa, as special adaptations to a changed 

 mode of life. They appear primarily to serve a protective 

 purpose, ensuring the persistence of the race, since they 

 only appear in extreme climates on the approach of 

 drought, and in cold ones on the approach of winter. 

 As a secondary function they serve for the dispersal of 

 the species ; some are light enough to float down a 

 stream, but not too far, so that there is no danger of 

 their being carried to sea ; others, which are character- 

 ized by large air-chambers, are possibly distributed by 

 the wind. 



Semal Both sexual elements may be formed in the 

 repro- game individual, e.g., Oscarella lobularis, Grantia 

 auction, raphan^ an( i many others ; but even in herm- 

 aphrodites one or other element usually occurs to 

 excess in different individuals, so that some are F , G 

 predominantly male and others predominantly 



granules ; at first they exhibit lively amoeboid movements, 

 but later pass into a resting stage. The cavity of the 

 mesodenn within which they are situated becomes lined 



FIG. 24. Spermatozoa, a-*, Development of spermatozoa in Sycatidra raj*- 

 anus, highly magnified ; Ik, mature spermatozoa. After Polejaeff (x7S>2). j, 

 A sperm ball in Osmrdla Mnlarii (x 500) ; 1; an isolated mature spermatozoon. 

 After Schnlze(xSOO). 



by a layer of epithelium, which may not appear, however, 

 till a late stage of segmentation. In Eutpongia qfficinalii 

 the ova occur congregated in groups within the mesodenn, 

 thus presenting an early form of ovary. The spermatozoa, 

 which also develop from wandering amoeboid cells, are 

 minute bodies with an oval or pear-shaped head and a 

 long vibratile tail (fig. 24 ). Each amoeboid cell produces 

 a large number of spermatozoa, which occur in spherical 

 clusters or sperm-balls. The heads of the spermatozoa, 

 as in the Metazoa, are produced from the nucleus of the 

 mother-cell, the tails from the surrounding protoplasm. 

 The development in detail is upon two plans. In Grantia 



b, c, ovum seg- 



i. Development of a calcareous sponge (Syoandro raplantu). 



mented, b, as seen from above, e, lateral view ; d, blastosphere ; , amphiblastula ; /, com. 



t _ i r < mencement of the invagination of the flagellated cells of the amphiblastula ; a, eastrala 



lemale. rolejaetf lOUnd only One SUCh male lOrm attached by its oral face ; , j, young sponge (Ascon stage),-*, lateral view, ;, as seen from 



to 100 female forms in Grantia rapkanus. In above - After Schuize. 



Other sponges Reniera fertilis, Evspongia officinalis the j raphanus (rj) the nucleus of the mother-cell divides into two 

 sexes are distinct. The ova develop from archajocytes or (%, 24 *) one , c **"> resulting daughter nuclei undergoes no 

 ,., ,, 1.-1- j further change, but with a small quantity of peripheral protoplMB 



wandering amoeboid cells, which increase m size and ac- forms a " covlr-cell" to the other or primitiveVperm nucleus and its 

 quire a store of reserve nourishment in the form of yolk | associated protoplasm. The sperm nucleus repeatedly divides, with- 



