414 Prof. M. Schultze on Polytrema miniaceum. 



of the same book : — " The calcareous shell of the Rhizopoda is 

 lined by a delicate organic membrane. If a Rotalia, Rosalina, 

 or Textularia, living or preserved in spirit, or dried with its 

 organic contents, be dissolved in dilute acid, there is observed 

 within the above-mentioned organic foundation of the calcareous 

 shell, a thin, but sharply contoured, homogeneous membrane, of 

 a more or less brown colour, which lies close to the former, and, 

 like it, is penetrated by pores. This uniformly lines all the 

 chambers, and is continued through the siphons of the septa 

 from one to the other. It is only in the last and youngest cham- 

 bers, which during life are nearly colourless, that this membrane 

 is so delicate that one might suppose it to be formed only simul- 

 taneously with the reception of colouring matters into the ani- 

 mal contents.^^ This description applies perfectly to the organic 

 lining of the chambers of Folytrema as here represented (tig. 8). 

 It forms a delicate, brownish, empty tube, occupied only at its 

 lower part with granular remains of the body of the animal, 

 which remained after the solution of the lime, but is not the 

 organic foundation of the shell itself. The latter contains so 

 little organic substance, that, in dissolving it in acids, I never 

 could succeed in obtaining a coherent portion of membrane. 

 But the place which it occupied, and its thickness, may never- 

 theless be recognized in shells which have been carefully dis- 

 solved, and, indeed, in the organic linings of the pore canals 

 which penetrate the latter. As the cavities of the chambers are 

 limited by a dense organic membrane, the tubules which pass 

 straight through the thick shell, and which are rather wide in 

 Polytrema, are also lined with a similar membrane. Some such 

 delicate tubes, isolated by the acid, are shown in figure 8, lying 

 partly upon and partly near the membrane; others, in much 

 greater number, are shown in their natural position in figure 4; 

 and figure 9 represents some similar tubes, of remarkable length. 

 They therefore correspond with the pore canals passing through 

 the shell, represented in figure 3. They exhibit the same differ- 

 ence of length according to the thickness of the shell, and show 

 the same peculiar segmentation, which seems to be connected 

 with the stratification of the shell. 



The brownish-red contents of the chambers, lastly, show no 

 other structure than that which I have described for the con- 

 tents of the shells of Polythalamia. 



If, however, from the structure of the calcareous walls of the 

 shell of Polytrema, and from the nature of its contents, the no- 

 tion that we might have in it a Sponge with a reticular calca- 

 reous framework is to be regarded as set aside, and it is rather 

 proved that Polytrema approaches the Polythalamia in every 

 respect, we have still to settle the question as to how the siliceous 



