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 Difflugie 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 ameeboid movements, and developed pseudo- 
podia”’; in fact it had a strong resemblance to 
Pelomyzxa, 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 tbat 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 crispw and those of 
Carpenter on Orbitolites tenwissima and O. 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. 
