114 M. E. Iliickel on the Ori/ani'.~a(ion of Sponges, 



of organic substance (nioditicd jn-otojilasni). In many Calci- 

 spongijB the carbon-compound takes so considerable a sliare in 

 the tbrmation oi the skek^tal jiarts, that the hitter, alter the 

 extraction ot" the carbonate ot" lime by muriatic acid, remain 

 quite unchanged in form and size, whilst only a slight residue 

 of molecular calcareous dust is left after calcination. 



The forms of the skeletal parts or spicules in the Calci- 

 spongiiv are, as is well known, by no means so multifarious 

 as in the Silicis]iongiie. Only the four following fundamental 

 forms occur, with various modiiieations : — 1. Sim])le spicules 

 (linear, cylindrical, or fusiform), frequent. 2. Two-limbed 

 s})icules (forked or hooked), very rare. 3. Three-limbed or 

 triradiate spicules (with equal or unequal limbs and with 

 equal or unequal angles), by far the most frequent, and at the 

 same time the form most characteristic of the Calcispongiai. 

 4. Four-limbed or quadriradiate spicules (the fourth ray of 

 which usually projects freely into the canal-system). The 

 different modifications of these four fundamental forms, which 

 have hitherto occupied the attention of the observers of the 

 Calcispongire more than all the rest of their organization, will 

 be completely described in my monograph. 



That the Calcispongice of all living s))onges are most nearly 

 allied to the corals, may be inferred in tlie first place even 

 from the calcareous nature of the skeleton in the two groups. 

 But to this may be added very interesting homologies in the 

 special differentiation of the canal-system in the most highly 

 developed forms of the Calcispongiee, which in part directly 

 ap])roach the sim])ler forms of corals even by the formation 

 of antimera*. We may therefore be allowed, in conclusion, 

 to glance at the sfejJs in the evolution of the canal-system 

 in the Calcispongiae. 



At the root of the whole system (or, M'hat is the same thing, 

 of the genealogical tree) of the Calcispongiaj stands the remark- 

 able Prosycuniy the little calcareous sponge whose canal-system 

 consists merely of a stomachal cavity with a mouth-opening. 

 Next to this comes Oh/nthiis^ a siinjde " person " with stomach 

 and mouth-opening, but the stomachal Avail or body-wall of 

 which is permeated by perfectly simple ])ores. These cutaneous 

 pores are simple breaches in the parenchyma, which perforate 



• Hackel applies the term '■'■ antimera^^ to tlie "homotypic orfrans " of 

 Bronn — that i.s to say, to those segments of the body, placed side by side, 

 of which each contains " all or nearly all tlie essential parts of the body 

 of the species." The segments of the liadiate animals, as indicated in 

 the text, furnish the most striking examples of this nicjde of formation. 

 Where the repetition of parts occurs in consecutive segments (as in the 

 Annulosa), these are called " mctamera " by Iliickel. — \V. S. D. 



