Distribution of Sar.cammina sphserira, etc. IS 



to accommodate the growing organism, a part at a time, we should 

 surely find such transitional stages and irregularly formed shells 

 in the vast mass of material at our disposal, but tliis has not been 

 the case. The one thing most noticeable in a Saccammina gather- 

 ing is the atonishing regularity and symmetry of the specimens. 

 Abnormal or malformed specimens are of such rare occurrence 

 that they are very difficult to discover. The growth, however it 

 proceeds, must be practically simultaneous throughout tlie test, 

 and in this matter the monothalamous Foramiiiifera cannot be 

 compared, as Dr. Rhumbler (6', p. -472) does compare them, with the 

 polythalamous forms. 



Dr. Rhumbler has sought to find storehouses of building mate- 

 rial to be at some future time incorporated in the growing shell, 

 in the form of fistulose projections of the shell -wall, which he calls 

 (6', p. 485) pseudopodial- tubes (Fseudopodialrohren), through which, 

 tnough they are firmly constructed and consequently unretractile, 

 the animal can extrude its pseudopodia and gather sand-grains for 

 subsequent use. He founds this hypothesis upon three specimens 

 which be figures (6, plate 22, figs. 18, 23, 24) ; and he adds (p. 488) 

 " The further fate of these extensions would probably consist of an 

 insertion (taking in) of its building stones into the disintegrating 

 genuine w^all of the remainder of the test." We regard these fistu- 

 lose excrescences as mere abnormalities ;* if they were a constant 

 feature of the shell growth they would be a common occurrence 

 in all dredgings in which Saccammina is abundant, which they 

 are not. When they occur, they are as firmly constructed as the 

 shell- wall itself, and the suggested process of forming and re- 

 disintegrating them for use in expanding the shell- wall would be 

 in direct opposition to the economy of Mature. Economy of cement 

 is one of the fixed rules of construction in the arenaceous Fora- 

 minifera, and such a process as Dr. Rhumbler suggests would 

 involve a highly unnatural waste both of effort and material. 



The processes of test-development or shell -grow^th in Saccam- 

 mina and Psammosphsera are conjectural, inasmuch as no one has 

 as yet observed the development of the living animal. Two 

 theories exist : (1) that the animal from time to time abandons its 

 test, and forms a new one of larger dimensions ; and (2) that it 

 possesses the power of re-dissolving the cement with which the 

 constituent sand-grains are built together, and of re-depositing the 

 old material with additional matter so as to produce a larger shell. 

 The first theory may be dismissed as improbable ; such a method 

 of growth is unknown as a vital process in any of those genera in 

 which the process of reproduction and development has been ob- 

 served, as Dr. Liicke {9, p. 20) has properly remarked. Moreover, 

 if the young shells were, abandoned at successive stages of growth, 



* In many cases which we have observed, these projecting tubes when broken 

 open proved to be tests of Beophax scorpiurus and other Foraminifera, which had 

 been incorporated in the shell-wall as building-material. 



