78 Dr. G. 0. Wallich on the Process of 



aperture of the last-formed chamber, after j;he fashion of Gro- 

 mia *. 



Of the highly important office performed by this outer layer, 

 there appears to be no room for doubt. Owing to this import- 

 ance, and the misconception that would inevitably arise were it 

 to be regarded as made up of ectosarc alone, I have thought it 

 necessary to distinguish it from the rest of the soft mass by 

 the name of chitosarc (^^treov, a coat). But it must be ex- 

 pressly understood that this layer is not distinct in constitution 

 from the rest of the sarcode, but formed out of it, and (as in the 

 case of the naked Rhizopods) continually intermingling with 

 the internal portion by amoebasis. It is through the agency of 

 the internal surface of this layer or chitosarc that the increase in 

 the thickness and strength of the shell is effected, the various 

 complicated canal- systems formed, and all secondary deposits 

 and the entire series of surface-markings of the Foraminifera 

 producedf. 



This layer would seem to be present in all the testaceous genera 

 of Rhizopods. In Gromia it has long been recognized, and sup- 

 posed to be altogether derived from a reflexion of the sarcode-mass 

 issuing at the mouth of the test. In the Polycystina, as in the 

 Foraminifera, it undoubtedly produces all the beautiful sculp- 

 turings for which these organisms are so celebrated. The growth 

 of the siliceous framework of theAcanthometrina and Dictyochidse 

 is almost wholly dependent on its presence; whereas in the highest 

 order of Rhizopods, namely the Proteina, it is extremely proba- 

 ble that it occurs also in all the testaceous genera, although, 

 from the greater differentiation of the sarcode-substance gene- 

 nerally, it is more delicate and less easily traceable. In this 

 order I have not seen it ; but there seems reason to suspect that 

 in Euglypha and indeed all the Lagynidse, and also in the tes- 

 taceous Amoebans (as in Diffiugia and Arcella), it is not only 

 reflected from the main orifice, but escapes partly through the 

 minute pore or pores which are distinctly visible at the apex of 

 the test in Euglypha, Cadium, Protocystis (Wall.), and Diffiugia. 

 In the latter genus the pore is at times produced into a hollow 

 cylindrical tube of some length, as shown in my paper on Amoeba, 



* For reasons which will be given in a later portion of this paper, I am 

 inclined to beUeve that the test of Gromia may not be strictly imperforate. 



t The presence of an outer investing film of sarcode in certain Foramini- 

 fera appears to have been recognized by Dr. Carpenter and Prof. Schultze. 

 In the * Introduction to the Study of the Foraminifera ' (p. 128), the former 

 author accounts for the exceptional structure of Dactylopora by ascribing 

 its formation to this outer film, and cites Gromia as an example in which 

 it is reflected back over the entire test, from the sarcode-body protruded 

 through the main aperture. 



