446 



closed, with its posterior corner situated at the dorsal anterior position, 

 and creaves the water with its sharp, lower margin. 



We suppose that clams come near the surface of sea-bottom before 

 slipping and secrete mucus which being lighter than the sea- water is 

 carried obliquely upward by tide as it is secreted. When the mucous 

 string is secreted long enough to balance the weight of clam in water, 

 the clam slips out of the bottom and is carried by current rather quickly. 

 The clam seems not to float high in water, but only a little above the 

 bottom. 



Late in spring Meretrix meretrix secretes mucus rather profusely, 

 and when the weather is calm and warm the mollusc seems to move to- 

 wards the deeper part of water at the time of the spring tide by means 

 of mucous strings. It is told that these mucous strings are sometimes 

 so abundant that anglers are annoyed great deal from these strings 

 twisting round their lines. This migration takes place perhaps to seek 

 water of mild temperature, avoiding severe heat of summer in a shallow 

 water. Slipping clams are mostly observed near the place where little 

 water remains at the time of the spring tide. 



The drifting or slipping clams when caught by any obstacle seem 

 to settle there, at least for a while. Thus we frequently find many clams 

 crowded at the root of fagots erected for the culture of oyster or Por- 

 phyra, a kind of sea-weed. We never hear or observe clams moving 

 towards the shore by this mode of locomotion. Recently I have heard 

 from an old fisherman in Kusatsu near Hiroshima that fishermen of the 

 village now cultivate this clam by building a fence of about 30 cm at 

 the deeper boundary of the culture-ground. The fence obstructs the 

 migrating clams, but fishermen are obliged often to collect the slipped 

 molluscs at the root of the fence and to distribute them again in the 

 culture-ground. 



Tokyo, Nov. 29,1912. 



4. Über die Herkunft von Sporn und Kastanie der Equidae. 



Von P. E. Keuchenius, Utrecht. 



eingeg. 24. Dezember 1912. 



Die Ansichten Hintzes (Zool. Anz. Bd. 35 Nr. 12—13, S. 372) 

 über die Herkunft von Sporn und Kastanien der Equidae haben Dr. 

 H. A. Vermeulen, Prosektor am Anatomischen Institut der Tier- 

 arzneischule zu Utrecht, veranlaßt, die Ontogenie dieser Hornbildungen 

 des Pferdes zu untersuchen (Tijdschrift voor Veeartsenijkunde 3 e Abi. 

 Febr. 1911). 



Vermeulen gibt in seiner Abhandlung eine Beschreibung der von 



