410 Prof. M. Schultze on Polytrema miniaceum. 



The apices of the lobes and combs of the surface also bear similar 

 shallow depressions. But, on these, orifices passing further in- 

 wards are very frequently met with — the commencement of 

 canals which penetrate the interior. These orifices I do not 

 regard as natural, but as produced by the breaking off of the 

 processes or by the erosion of the surface. 



Dr. Krohn had the kindness to give me some Polytremata 

 which he had collected on seaweeds at Nice and brought with 

 him in a dry state. At the first glance of these I was vividly 

 reminded of the Polythalamian structures from the Philippines, 

 described by me as Acervulina acinosa*, which are of the same 

 size and colour, and occur under similar circumstances, but pre- 

 sent a somewhat different relief on the surface. Krohn had 

 already ascertained that Polytrema exhibits a structure of the 

 calcareous walls similar to that presented by the thick-walled 

 Polythalamian shells. But what had especially attracted his 

 attention was, that in Polytrema it appeared that siliceous spicules 

 occurred constantly, as in the Sponges, sometimes projecting 

 freely from the above-mentioned orifices at the apices of the 

 lobes, but in other cases only becoming visible when the calca- 

 reous shell was crushed. 



The examination of the dry specimens given to me at once 

 confirmed the similarity of the structure of the calcareous walls 

 with that of the thick-walled Polythalamian shells, and at the 

 same time the occurrence of sponge-spicules in the interior of 

 the Polytrema. These were chiefly siliceous, and exactly of the 

 structure of ordinary sponge-spicules, awl-shaped, with a fine 

 axial canal, and either pointed at both ends or knobbed at one 

 of them. (PI. VII. fig. 10.) A few calcareous spicules were inter- 

 mixed with them, as could be ascertained at once, and without 

 chemical tests, by means of the polarizing apparatus. Very 

 small spicules, hooked at both ends, also occur (fig. 10 a). Of 

 any organic matter occupying the cavity the dried specimens 

 showed mere traces. 



The interest attaching to the structures under investigation 

 could not but be extraordinarily increased when it appeared, 

 from further inquiry into the literature of the subject, that very 

 nearly allied structures had been examined by Dr. Gray, and 

 placed as intermediate forms between the Rhizopoda (Foramini- 

 fera) and Sponges. Gray found structures resembling Poly- 

 trema adhering to various marine productions (corals and shells), 

 and published descriptions of them under two new generic 

 names, Carpenteria and Dujardinia-f. By the examination of 

 thin sections of the calcareous shells of these parasitic organisms, 



* Ueber den Organismus der Polythalamien, p. 68. 

 t Ann. & Mag. Nat. Hist. ser. 3. vol. ii. p. 381 (1858). 



