1 68 NATURE AND AFFINITIES OF THE SPONGES. 



the feeding capacities of the sponge-monads, it may be here noted, that 

 the phenomena of nutrition are precisely identical with those exhibited 

 by the independent collared species, the selected pabulum being arrested by 

 the hyaline collar and carried with its circulating current into the body 

 of the animalcule. Examples are given at PI. VIII. Figs. 9 and 19, in 

 which the bodies of the neighbouring sponge-monads are rilled with ingested 

 and artificially administered carmine particles. Such functions of nutrition 

 are, however, not confined to the collared zooids ; the amoebiform units 

 or cytoblasts being equally capable, as shown at Fig. 41 of the same plate, 

 of ingesting solid pabulum. 



Examining the matter more closely, it has now to be shown that even 

 the special differences already cited as indicating a distinction between the 

 Spongida, independent collared monads, and ordinary Infusoria, are scarcely 

 more substantial than those found to exist between the more conspicu- 

 ously divergent representatives of the same groups or orders of the last- 

 named section. Taking, in illustration of this analogy, the very familiar 

 group of the Vorticellidae, we find in Vorticella, or more correctly, in the 

 stiff-stalked form Rhabdostyla and in the compound type Epistylis, the 

 precise analogues of the solitary collared type Monosiga and the social 

 genus Codosiga. Proceeding yet a step further, the slime- immersed colonial 

 type Ophrydium is beyond doubt comparable in a like manner to the 

 colonial slime-immersed genus Phalansterium. Beyond this it is not 

 possible, as yet, to institute a direct comparison, but, supposing that a 

 genus of colonial slime-immersed Vorticellidae should be discovered in 

 which the animalcules, instead of projecting directly into the surrounding 

 water through the peripheral surface of their common matrix, as obtains in 

 Ophrydium, were enclosed within chambers which communicated with each 

 other, and with the outer water, by a system of interconnecting canals ; 

 supposing also that all the spores, germs, encystments, or other repro- 

 ductive products remained embedded and developed to maturity within 

 the common matrix, a type of the Vorticellidae would be produced pre- 

 senting a parallel to Ophrydium precisely identical with what actually 

 exists between the most simple known sponge and Phalansterium* 



With the assistance of Plates VII. to X. it is now proposed to draw 



* At the eleventh hour, while going to press, the author has had the good fortune to light upon 

 a new and highly interesting representative of the independent collared series, that illustrates in 

 a yet more decisive manner the close relationship of this group to the Spongida. The type in 

 question, represented at PI. X. Figs. 20-30, and hereafter described under the title of Protospongia 

 Haeckeli, agrees with Phalansterium, so far as the zooids are immersed within a common gelatinous 

 matrix or zoocytium. The characteristic collars are, however, fully developed in place of being 

 rudimentary as in the last-named genus, while the inhabited gelatinous matrix is perfectly trans- 

 parent and homogeneous instead of densely granular. Within their matrix the zooids were observed 

 to assume various metamorphic amoeboid conditions, to multiply both by the process of binary 

 subdivision and by the partition of their entire mass into sporular elements. The resultants of 

 the last reproductive process commence their active existence as simple, minute, uniflagellate 

 monads, which project, as shown at Fig. 22 b b, from the periphery of the zoocytium side by 

 side with the adult collared units. This interesting species which, in its mature condition, corre- 

 sponds in a most remarkable and significant manner with a fragment of cytoblastema, with its 

 enclosed collared zooids, amcebiform cytoblasts, and sporular elements, of any typical sponge- 

 form, was obtained by the author in July 1 880, in water brought from the lake in Kew Gardens. 



