Prof. M. Schultze on Polytrema miniaceum. 415 



spicules get into the interior of the chambers. Are they pro- 

 duced in the Polytrema ? Have we to do with a transitional 

 structure between Rhizopods and Sponges, according to the no- 

 tion of Gray and Carpenter ? or are the siliceous spicules foreign 

 bodies in the Polythalamian, either introduced as food or belong- 

 ing to a parasitic Sponge ? With regard to this question, the 

 following observation is to be made : — The siliceous spicules 

 never occur in the above-described yellowish-brown animal con- 

 tents of the Polytrema, which are to be regarded as the Poly- 

 thalamian body, but always heside these, in an extremely destruc- 

 tible, transparent, colourless, finely granular substance, which 

 shows but little coherence, and is consequently distinct from 

 the former. During the solution of a Pohjtrema, with its ani- 

 mal contents well preserved, in a dilute acid, the difference be- 

 tween the two substances (the dense yellowish-brown one, and 

 that which contains the spicules) at once strikes the eye. The 

 latter is, however, usually so extremely small in quantity around 

 the siliceous spicules, which frequently lie as if quite uncovered, 

 that it is impossible to prepare it in connexion. It breaks up 

 as the spicules separate from each other ; and only traces of it 

 adhere to individual spicules or groups of spicules (fig. 10). It 

 is, moreover, of particular importance that by no means all speci- 

 mens of Polytrema contain spicules, and that, when these do 

 occur, they usually occupy only the peripheral chambers. The 

 twelve spirit-specimens of Polytrema which I examined by means 

 of dilute acids gave the following results : — Two of them had no 

 trace of siliceous spicules; all the chambers were completely 

 filled with the yellowish-brown substance, which diminished a 

 a little in intensity of colour towards the periphery. Three 

 specimens contained the remains of the yellowish-brown sub- 

 stance only in the more deeply seated layers ; nearly all the 

 chambers were full of siliceous spicules and the small quantity 

 of colourless organic substance belonging to them. All the rest 

 likewise contained siliceous spicules, but only in the peripheral 

 chambers, and often only in one part of them ; the greater part 

 of the interior system of cavities was filled with the brown sub- 

 stance, as shown in figs. 4-7. The siliceous spicules therefore 

 may be entirely wanting ; and when they occur, they never lie 

 in the true Polythalamian substance, but rather diffuse them- 

 selves, with displacement of the latter, from the periphery to- 

 wards the deeper parts; moreover they are imbedded in an 

 organic substance which does not appear to belong to the Poly- 

 thalamian body. The nature of the last-mentioned substance 

 certainly cannot be positively determined. It might possibly be 

 colourless Polythalamian substance. But, in opposition to this, 

 we have, in the first place, its want of solidity, its want of co- 



