456 PERCY SLADEN TRUST EXPEDITION 



believe that any of the spicules that are seen at the free edges are cast off when they have 

 served the purpose of a " temporary support for the extended pseudopodia " because the 

 greater number of them are firmly fixed into the solid calcareous skeleton and cannot be 

 withdrawn by pulling hard with a pair of forceps. Nevertheless there are far fewer 

 spicules in the calcareous substance, at a little distance from the free edges, than one would 

 expect to find if it is a fact that they remain unchanged as a matrix for the deposit of the 

 calcium carbonate. I am forced to the conclusion that in the process of the deposition 

 of the calcareous skeleton many of these siliceous spicules are dissolved. If there is not 

 some solution of the silex it is very difficult to account for the numerous fragments of 

 spicules that occur in the intralocular protoplasm. The spicules are taken up whole at 

 the ends of the branches and so far as I can observe at the ends of the branches only. 

 No spicules or fragments of spicules can be seen in the foramina that perforate the sides 

 of the main stem, base or branches. The fragments of spicules in the chambers therefore 

 must be derived from spicules taken up when those chambers were first formed and at the 

 growing points, or possibly passed down to them with the flow of protoplasm from other 

 chambers at the growing points. At the growing points however all the spicules seem to 

 be perfect, at least they are much longer than the diameter of the chambers and very 

 much longer than most of the fragments of spicules found in the older chambers. The 

 sponge spicules must therefore either be forcibly broken or partly dissolved after they are 

 incorporated into the substance of the organism and it seems to me that the view that they 

 are partly dissolved is the more reasonable of the two. 



It is difficult to account for the presence of the spicules in these Foraminifera. They 

 are quite constant in their occurrence and consequently it seems probable that they play 

 some essential part in the physiological processes of the species. The regularity of their 

 arrangement and the fact that, usually, very few other foreign bodies than the monaxon 

 siliceous spicules of sponges are found, show that they are not picked up at random but 

 selected from the mud in the neighbourhood and deliberately placed in position. 



That they are of foreign origin there can be no reasonable doubt. The sponges from 

 which they collect their spicules must live in the neighbourhood of the Polytremids, or the 

 Polytremids must live in a region where sponge spicules play an important part in the 

 formation of the sand or mud. Not infrequently the sponges cover a part of the Foraminifer 

 or, in some cases, completely overwhelm it. This is a special danger to which the Poly- 

 tremidse and some other calcareous organisms are exposed. Forty years ago there was 

 an interesting discussion on the origin of the siliceous spicules in these Foraminifera. 

 Gray (7) and Carpenter (2) maintained that both the siliceous spicules and the calcareous 

 skeleton are the products of the same organism, Max Schultze (15) and Carter (3) on the 

 other hand strongly opposed these views and maintained that the siliceous spicules are of 

 foreign origin. The controversy would be of little more than academic interest in these 

 days were it not for the fact that in a recent paper Kirkpatrick (9) has suggested that 

 Merlia, which he considers to be a sponge, does actually secrete siliceous spicules and a 

 calcareous chambered shell. Having had an opportunity of examining the structure of 

 specimens of Media and arrived at different conclusions to those of Kirkpatrick I will 

 postpone the discussion of this question to a subsequent paper. 



