I9 I 5-J Fauna of the Chilka Lake : Sponges. oq 



gemmules. In those parts of the sponge in which reproductive bodies are absent, 

 numerous spicules will be found with their heads embedded in the basal membrane 

 and their points projecting upwards. In most cases they do so at an angle less than 

 a right angle, but regular ascending columns of an entirety non-plumose character 

 can be distinguished. The lowest spicules in these columns project straight upwards 

 from the basal membrane, while the highest form brushes on the surface of the 

 sponge, where they are to some extent spla}red out. 



Otherwise the skeleton forms an indefinite network in which the strands are 

 formed mainly of single spicules and no very distinct fasciculation can be detected. 

 On and near the surface there are numerous horizontal spicules. 



Where gemmules are present the lower part of the skeleton becomes partially or 

 wholly disorganized, while the spicules tend to be massed in a horizontal layer a 

 little below the surface. As the cellular parts of the sponge also degenerate on the 



■■:■ •;■; >"- 



Fig. 6. — Suberitcs sericeus, Thiele. 

 Vertical section through the outer part of a sponge in phase B, showing gemmules, x ca. 10. 



production of gemmules and are less completely destroyed where furthest from these 

 bodies, the flesh is also massed together above and an "ectosome " distinct from the 

 ehoanosome is thus formed (fig. 7, p. 40). 



Gemmules are produced in large numbers. They form a single layer at the base 

 of the sponge firmly connected with the adherent basal membrane. They vary greatly 

 in size and shape but are always flattened at the base and strongly convex above. 

 Their horny coat is thin, but the fact that it is deposited in several layers can 

 sometimes be ascertained from its laminated structure. There is no foramen 

 (micropyle). The structure of the actual reproductive body is that usually found in 

 the gemmules of sponges. Spicules do not as a rule penetrate the gemmule-coat. 



Phase B. 



The skeleton in this phase is much more complex (fig. 4, pi. iv). The spicules that 

 have their heads embedded in the basal membrane form a dense irregular mass, all or 

 practically all of them meeting the membrane at an angle less than à right angle. 



