41 



whatever was to be found. It seems to me after what I mentioned above, 

 that crests can arise through bursts in the shell as well as quite inde- 

 pendently of these. In the last case ßubbel thinks of the penetrating of 

 parasites and this reali}' seems to me the most probable explanation, even 

 though this parasite is not always to be found. That we find abnormalities, 

 crests, oil-stains, pearls etc., so often, though not always, near the top, 

 apex, and near the obtuse side of the shell can perhaps be put down to 

 the fact that near the mouth of the animal is a spot where the edge of 

 the mantle has not grown against the shell. So then there is for parasites 

 and other strange bodies an opportunity to jjenetrate into the cavity be- 

 tween mantle and shell. Everywhere else the edge of the mantle is firmly 

 grown together with the shell and there is no question of penetrating — . 



After all I have said before, the question, whether we sometimes 

 find regenerates and deformations also in the shells along our beach, 

 seems quite obvious. 



In Mytilus edulis, Buccinuiii undatum^ Mactra stuUorum, Solen 

 pjisis, Fusus antiquus and Ostrca edulis I found indeed regenerates. 

 In Tellina, Donax, Mya, Cardiuuf, Pholas, Pecteii and Natica however 

 I have never been able to find a trace of them. As far as I can judge 

 the matter now, regenerates occur most in 2Iyfilas edidis, besides rather 

 often in Buccinum undatum. Much rarer in the other forms mentioned. 

 All the shells mentioned are from the North Sea and found at: de Koog 

 (Texel), den Helder, Huisduinen, Ymuiden, JSToordwyk a./Z., Katwyk 

 a./Z., Scheveningen, Kykduin, Hoek van Holland and Domburg. The 

 information about Ostrea edulis I owe to Prof. Dr. G. C. J. Vosmaer, 

 to whom I here wish to render thanks again for his interest. Prof. Vos- 

 maer told me that, when Ostrea has been impaired by boring sponges, 

 Cliona celata, the oyster reacts upon it by repairing the bored holes 

 and closing the openings in this way. So Ostrea too is able to make 

 regenerates. The greatest number of examples of regeneration I 

 examined in Mytilus, viz. 8. The damage of one of these 8 cases had 

 been caused by Cliona and is as far as regeneration is concerned the 

 same as the cases of Ostrea just mentioned. In the shells of Mytilus 

 are often found dents, on the outside, which then cover each other 

 with the equivalent vaults on the inside. This phenomenon however 

 has nothing to do with regeneration, though it may sometimes seem so. 

 I do not know the cause of it. All the 8 regenerates were small, com- 

 plete and only in 1 case accompanied by the formation of a few little 

 pearls, exactly in the mussel which showed the greatest damage and 

 the biggest regenerate. There was no preference as to the place of the 

 damage. Here too I found, as in Anodonta, the regenerate larger than 

 the hole to which it belonged. The secondary periostracum, on the re- 



