XVII. SPONGI^E. 
20 Spong. 
stages. The first step in the development of the bud is the specialization 
of a number of the indifferent cells to become scleroblasts which secrete 
macroscleres, monaxons and spherasters [see n, b, iv, c]. The next 
differentiation of the archseocytes, at a time when the bud is beginning to 
project from the surface of the sponge, gives rise to transitional formative 
cells, from which are derived, by further specialization, the epithelial, 
fibrous, and connective-tissue cells of the dermal layer and the scleroblasts 
of the microscleres (chiasters). The bud when set free is solid, and is 
composed of the classes of cells and spicules already mentioned, and of 
archseocytes, but contains no flagellated chambers or collar-cells. The 
gastral layer originates at this stage by rapid division of centrally placed 
archseocytes into small elements, the mother-cells of the choanocytes, 
disposed at first in groups or cell-islands, which join together to form a 
distinct medullary region of the bud. In the medulla the rudiments of 
the canal-system arise as a number of spaces and lacunae, lined at first by 
the mother-cells of the choanocytes, but as the canals increase in size, cells 
of the dermal layer push their way in to form a lining to them. The 
gastral cells become aggregated round small cavities, the flagellated 
chambers, where after further cell division they give rise to an epithelium 
of collar-cells. The bud becomes fixed at the time the canal-system is 
completely developed. The origin of the bud resembles that of the ovum 
in being derived from a number of archseocytes, but differs in that all the 
individual archseocytes contribute to the composition of the bud, while in 
oogenesis one of them, the ovum, absorbs the others as food-material. As 
in the embryonic development of sponges, the differentiation of the cells 
furnishes at first two germ-layers, dermal and gastral, and a close 
parallelism between bud and embryo is also seen in the development of 
the canal-system and of the tissue-elements ; differences, on the other 
hand are seen (1) in that the dermal layer surrounds the gastral layer 
directly in the bud, but in the embryo only comes to do so after a meta¬ 
morphosis with inversion of the layers ; (2) in that the flagellated cells 
(choanocytes) are the first elements set apart in the embryo, the last in 
the bud. The course of development by budding is not, however, to be 
contrasted with that of embryonic development as something peculiar and 
distinct. Maas (38). 
(c) Regeneration. —In Regadrella okinoseana , with consequent mal¬ 
formations, p. 250, and in Euplectella imperialism pp. 83 & 84; in E. 
marshalli, pp. 200 & 201 ; in Walteria leuckarti, p. 292 ; Ijima (29). 
F. Miscellaneous. 
(i) Technique. —Practical study of Sponge-structure ; Ivukenthal 
(34) pp. 36 & 44.—Methods of collecting and preserving sponges ; Anon 
(4) pp. 6 & 7.—Methods for preserving Sponges for Histology; Bolles-Lee 
(8) pp. 489 & 490. 
Methods of collecting Hexactinellids and other Deep-Sea Animals in the 
Sagarni Sea, by means of the “dabo-line” or long line for deep-sea angling, 
pp. 16-31.—Methods for the preservation and histological study of 
Hexactinellids, pp. 32-36; Ijima (29).—Methods of preserving Tethya for 
study of the budding; Maas (38) pp. 265 & 266. 
Methods for investigating the minute structure of calcareous spicules, 
p. 271 ; of siliceous sponge-spicules, pp. 236, 252, 257 & 262 ; Butschli (9). 
—Preparation of fossil sponge-spicules from the chalk; Schrammen (50) 
p. 2. 
(ii) Economics. —Bath-Sponges ; their structure, pp. 256-261; 
varieties and distribution, pp. 261-267; reproduction, pp. 267-270; 
