577 
Briefly, I came to exactly the same results as Rubbel, independent of 
him. The regenerates which I saw consisted of all three layers, perios- 
tracum, prismatic layer and layer of mother-of-pearl, and they were 
almost as firm as the shell itself. So I cannot agree with Br ehms 
Tierleben, when on page 183 he speaks about »notdürftig ausgeflickt«. 
In my opinion the regenerate could not be more complete. 
In the formation of the layer of mother-of-pearl on the regenerate, 
I saw some other things which neither Rubbel nor Rassbach describe. 
The layer of mother-of-pearl seems to be set off on the prismatic layer, 
on the »polygonale Felderung«, in figures which resemble very much 
what we call »frost-flowers«, in winter. Little pieces of the regenerate 
which were thin and transparent enough clearly showed the three suc- 
cessive layers. Where the figures of mother-of-pearl were to be seen, 
nothing or hardly anything, as was to be expected, could be seen of the 
»polygonale Felderung«, of the prismatic layer. The layer of mother- 
of-pearl of the regenerate further showed a great number of very small 
pearls that had grown to it; these were also found on the mother-of- 
pearl of the shell itself, near the regenerate. I have often noticed such 
a connection between regenerated damages of a shell and the occurrence 
of little pearls on the regenerate, or near it. Meanwhile both can occur 
independently of each other. The reverse however is more usual. With 
the experiments of regeneration which Rubbel and Rassbach exe- 
cuted, pieces were sawed out of the shell of the living animal, and the 
openings were generally stopped with cork or paper, covered with cel- 
loidin or layers of shellac. Of course the shells which I found in nature 
did without any protection and this is not without influence on the for- 
mation “of the regenerate. Especially the periostracum that is being 
formed, is then exposed to detrimental influences. In the first place, a 
shell, the hole of which is stopped with paper etc., will probably rege- 
nerate much quicker than a shell left without any covering whatever. In 
my opinion the penetrating of sand etc. will rather arrest the process of 
regeneration and perhaps even damage the periostracum which at first 
is exceedingly thin. This is altogether out of the question with shells 
protected with paper etc. On the newiy formed periostracum of my 
specimens I observed that its surface was folded and wrinkled over and 
over, while further the periostracum, on the outside, so-on the side 
turned away from the prismatic layer, was covered, by pieces, with a 
white crust of lime. This crust of lime is therefore directly connected 
with the grains of sand etc. that penetrate into the shell through the 
hole. I found many grains of sand fixed in this crust and the greater 
part of the loose grains of sand was wholly or partly surrounded by lime, 
Some parts of the periostracum were quite covered with this layer of 
37 
