8 M. E. Hackel on the Organization of Sponges^ 



Coelenterata can be more completely establislied upon the 

 basis of extended ontogenetic and comparative anatomical in- 

 vestigations. 



That the essential agreement in the internal organization of 

 the sponges and corals, their actual homology, has hitherto 

 been for the most part overlooked is due, among other things, 

 to the fact that the most accm'ate anatomical investigations of 

 recent times (especially those of Lieberkiihu) took their start 

 from the two best-known and commonest forms of sponges — 

 namely, the freshwater sponge {Spongilla), which belongs to 

 the group of the true siliceous sponges, and the common sponge 

 {Etitjwngia), belonging to the group of horny sponges. But 

 these very two forms of sponges differ in many respects con- 

 siderably from the original and typical structure of the entire 

 class, have been in many ways modified and retromorphosed 

 by adaptation to special conditions of existence, and therefore 

 easily lead to erroneous conceptions, especially as their inves- 

 tigation is comparatively difficult. 



On the other hand, among all the sponges, no group appears 

 better fitted to shed full light upon the typical organization 

 and the true relations of affinity of the whole class than the 

 legion of the Calcispongise. Lieberkilhn has already expressly 

 acknowledged this in his ' Beitrage zur Anatomic der Kalk- 

 spongien ' (1865), and endeavoured, from the results obtained 

 from the Calcispongia3, to render the other sponges more in- 

 telligible. 



This applies in the first instance even to the individuality 

 of the Calcispongiee, which is adapted, in a far higher degree 

 than that of most other sponges, to elucidate the difficult tec- 

 tology or theory of individuality of the sponges. Reserving 

 the circumstantial statement of these conditions, Avhich are 

 equally interesting and important, for my monograph of the 

 CalcispongijB, I will here cite only the result of my special in- 

 vestigations upon this point. This consists essentially (leav- 

 ing out of consideration some modifications) in a confirmation 

 of the opinion quite recently put forward by O. Schmidt, that 

 every part of the sponge-body which possesses an excurrent 

 orifice [osculum) is to be regarded as a distinct " individual." 

 This " true individual " of the sponge-body I denominate, in 

 accordance with my theory of individuality, a " person ;" and 

 every sponge-body that consists of two or more persons (i*. e. 

 that possesses two or more oscula) I denominate a " stock " or 

 " cormus." The special limitation of these two ideas, which 

 are rendered necessary by the peculiar conditions of indi- 

 viduality of the sponges, I reserve for my monograpli. There 

 are consequently simple (solitary or monozoic) and compound 



