58 



GEODIA VARIOSPICULOSA. 



lie at, or just above, the lower limit of the sterraster-armour layer; the cladomes 

 of the anatriaenes and mesoproclades he at different levels. The sparse high 

 spicule-fur is composed of the distal, freely protruding parts of mesoproclades, 

 chiefly mesoprotriaenes, and large anatriaenes. On small parts of the surface 

 of the specimen of var. micraster freely protruding orthoplagiotriaenes occur. 

 I do not believe, however, that these spicules normally take part in the formation 

 of the fur, but consider that the sponge must, at a previous time, have received 

 some injury in the places where these spicules are found. 



In the inner layer of the cortex numerous small styles and minute anaclades 

 (Plate 18, figs. 8c, 26e) are observed. These are situated radially or obliquely, 

 rarely pariitangentially. Some of them form groups, others are scattered singly. 

 Some lie between the bundles of large spicules (Plate 18, fig. 26e), others form 

 clusters around them (Plate 18, fig. 8c). In the thin walls of tissue separating 

 the subcortical cavities strand-hke rows of these small spicules occur. They are 

 also met with in small numbers in the sterraster-armour layer. The low dense 

 fur, referred to above, is entirely composed of these spicules. In the spicule- 

 fur of var. intermedia and also in that covering the parts of the surface with thick 

 cortex in var. micraster the styles predominate greatly, only a few minute ana- 

 clades being here scattered between the dense masses of small styles. In the 

 low spicule-fur covering the parts of the surface of var. micr'aster which lie at a 

 lower level and below which the sterraster-armour is thin, the minute anaclades 

 are very abundant, more numerous than the small styles (Plate 18, fig. 24a). 

 The spicules forming this low dense fur protrude for the greater part of their 

 length beyond the surface of the sponge; the pointed ends of the small styles 

 and the cladomes of the minute anaclades being situated distally and free, the 

 rounded ends of the styles and the acladomal ends of the minute anaclades 

 being situated proximally and implanted in the sponge. The manner in which 

 these minute dermal styles and anaclades are distributed shows that they are 

 formed in the distal layer of the choanosome or the proximal layer of the cortex, 

 that they travel up from this, their place of birth, to the surface, first, up to the 

 sterraster-armour layer, slowly, then, through the sterraster-armour layer, 

 rapidly, and that their movement in this distal direction is retarded to a great 

 extent or quite discontinued on their reaching their final position in the low 

 spicule-fur, where they remain for a considerable time. 



Four kinds of microscleres occur; large oxyasters, smaller oxysphaerasters, 

 small strongylosphaerasters, and sterrasters. The large oxyasters are confined 

 to the choanosome. They are not uniformly distributed; in the distal zone of 



