Spinning Shtg.i and Snaih. 431 



plays such a part that it might be asserted that the animals 

 crawl upon their slime. L<>t us ima^rine a Limax or an 

 Arion that possessed no mucus. Every grain of sand, every 

 pine-needle, every dry fragment of a plant upon the ground 

 would to a certain extent give way, and progression, though 

 not exactly impossible, would be greatly impeded. The 

 mucus in the first place cements everything together into a 

 relatively firm whole. In the case of the mussels also it 

 serves a similar purpose. 



If we imagine the bridge of mucus extended, we have the 

 rope of slime that young Helieidje and the species of the 

 genera Ilyalina and Vitriria are capable of forming. In the 

 case of these creatures, if their weight is not too great, the 

 mucus is tough enough to be drawn out into short threads 

 which support the animal, though they are certainly con- 

 siderably thicker than in the case of Liinax. In the case of 

 Vitrina pellucidd I measured threads of from 15 to 20 ram. 

 in length ; in that of young specimens of Arion the thread 

 gave way on reaching a length of 5 mm., and older individuals 

 fell before the foot had completely left the support. 



It follows that from Vitrina to Lima.v we see an advance 

 in the process of thread-formation. In order to be capable of 

 being drawn out into durable threads, the mucus must be 

 extremely tough and harden quickly. In the case of Agrio- 

 limax and Liinax it possesses these properties in a liigh 

 degree. Now since various authors (Leydig, Simroth, Clessin, 

 and Goldfuss) state with regard to Amalia that the mucus 

 is excessively tough, and that byssus-like threads occur in it, 

 it may be expected tliat the animals of the genus in question 

 possess the capacity of tiiread-drawing in a much higher 

 degree than those of other genera. Simroth [apud Clessin, 

 * Mollusken-Fauna von Oesterreich-Ungarn und der Schweiz,' 

 1887, p, 51) writes as follows concerning the mucus of Amalia 

 robici'. — " If it is proved by Leydig that the mucus of the 

 species of J »jrt//a owes its varnish-like viscosity to byssus- 

 like threads, we here have actual byssus. Widely scattered 

 on the body, closer together on the sole of the foot, but 

 especially in the groove which bounds the locomotor median 

 area, there projects a series of whitish pointed threads, which 

 are apjiroximately equal to this median area in length." 



In eonelusion,! would |)oint out that gardeners should take 

 a special, although certainly not a benevolent, interest in the 

 spiiming slugs. Undeniably the best method of protecting 

 valuable plants from being eaten by slugs and snails is to 

 render it imj)ossible for the animals to obtain access to them 

 by placing the plants in saucers tilled with water. But this 



