INTRODUCTION. 21 



were united to each other by a narrow, transparent, 

 and originally quite colourless, connective substance, 

 which only some days later began to acquire a dark 

 brownish hue. 



Another result of Verworn's experiments was to 

 show that the Difflugian shell, once injured or removed, 

 is incapable of restoration. The whole of the shells of 

 several individuals were removed without injury to the 

 protoplasmic body, and whilst the Difflugi& lived a 

 considerable time some of them about three weeks 

 and behaved quite normally, taking up sand-grains, 

 which collected in the interior of the protoplasm, no 

 trace of a regeneration of the shell was observed ; the 

 body-surface did not present the least excretion or 

 deposition of solid matter. It was " rather soft, per- 

 formed amaeboid movements, and developed pseudo- 

 podia"; in fact it had a strong resemblance to 

 Pelomyxa, the likeness being still further increased by 

 the greyish-brown coloration, the incepted glass 

 granules, and the great number of nuclei. 



The obvious conclusion is that in all the Mono- 

 thalamia the test originates at the moment of fission 

 and is completely finished at the separation of the new 

 individual from the parent. The protoplasmic body 

 then ceases to have any secretory relations with the 

 shell : the faculty of shell-formation has ceased. 



Upon a review of all the circumstances, and having 

 regard to the fact that whilst injuries to a mono- 

 thalamous Rhizopod test cannot be repaired, in the 

 polythalamous forms (the Foraminifera) this takes 

 place to the fullest extent, as shown by Verworn's 

 experiments on Polystomella crixjjd and those of 

 Carpenter on Orlitolites tenuissima and 0. complanata. 

 Dreyer, in ' Biologische Centralblatt ' (1889) endorsed 

 Verworn's conclusion that the faculty of a soft body 

 of secreting shell-material only continues so long as 

 the normal growth of the shell itself, from which, 

 then, the different behaviour of the mono- and poly- 

 thalamous Rhizopods may be explained. 



