576 
way. Such examples of natural regeneration under for the mussel nor- | 
mal circumstances do not often occur. Among the 414 shells, examined 
for this purpose, I found only 4, so about 1%. The example represented 
here, is probably Anodonta ventricosa Pfr.? I found the same with 
Anodonta cygnea and Unio pictorum. 
Fig. 1. 
All three with holes and regenerates about in the middle of the 
shell. In an other specimen of Anodonta ventricosa? I have found a 
fine regenerate on the back edge of the shell. There the newly formed 
periostracum showed some distinct lines of growth. This regenerate too 
Fig. 2. 
was perfect. As macroscopically the periostracum and the layer of 
mother-of-pearl of the regenerate in fig. 2 were clearly to be seen, so the 
prismatic layer could be shown microscopically. The latter showed it- 
self as a layer of white grains of lime, lying on the inside of the perios- 
tracum. Many grains were lying separately, others were melted together, 
and, in this way, showed the »polygonale Felderung«, which Rub bel 
(see top of the first page) describes on page 171. The concentric layers 
and the radiancy of the lime grains I saw very clearly, justas Rubbel did. 
