BAUNES: ON A DART IN HELIX ASPERSA. 285 



Another form of ergasidium is the dart of the Helicidae, etc., 

 variously known as the spiculum amoris, gyprobelum, and love dart. 

 This dart appears to be formed in less than a week, and is a crystalline 

 rod, which is slightly flexible, terminating in a fine point. The base 

 is enlarged to fit upon a conical tubercle at the bottom of the dart-sac. 

 A viscous secretion attaches it to the tubercle, and this also fills up 

 the interior, which is partially hollow. 



It used to be thought that it was hurled by one snail at another, 

 being launched into the air and buried in the tissues of the other 

 snail. It is thought now that, as the animals go round one another, 

 previous to conjugation, this dart is pressed out, and is so used to 

 stimulate the pair. In this way, owing to its loose attachment, 

 it may become fixed in the flesh of the other individual and be 

 drawn out. 



On May 7th, 1904, in a specimen of Helix aspersa which had not 

 previously been observed to conjugate, a dart was found in the body- 

 cavity. It was attached to the interior of the body-wall, almost 

 immediately above the muscle of the penis. This might be explained 

 in two ways. It may have belonged to another individual, and have 

 entered the body through the genital aperture, or it may have 

 belonged to the same individual, and, not being used, have worked its 

 way backwards, and have been replaced by the other dart, which was 

 found fully formed in the dart-sac. 



This second theory is supported by an observation made by 

 Mr. W. M. Webb, when the dart was found in the body-cavity of 

 three specimens of Helix aspersa which had been doiTQant for some 

 months. 



It would be of interest to know the fate of a dart which has entered 

 the body-cavity, by whatever means it may have got there ; but on this 

 point I do not believe anything is at present known. 



