COLLINGE : REVIEW OF THE ARIONID.E OF THE BRITISH ISLES. 59 



two branches, which pass to each side of the bucal cavity. There is 

 no retractor muscle to the lower portion of the vas deferens. Strong 

 retractor muscles, however, are attached to the receptaculum seminis 

 and the oviduct. The most prominent and distinguishing feature in 

 the nervous system is the two large dorsal nerves. There is no 

 penis or muciparous glands, and the spermduct never has a flagellum 

 attached. During copulation the female portion of the reproductive 

 organs are everted. 



Arion empiricorum, Fer., 1819. 

 = A. ater, Brit. Auctt. 



Body convex above, contracted and rounded in front, pointed 

 behind ; varies greatly in colour, being various shades of 

 black, brown, red, and yellow ; tentacles strongly granulated, 

 considerably enlarged at their bulbs; sole variable; foot-fringe 

 variable ; rugae large, keeled, and elongated ; shell absent, 

 mass of small calcareous granules. 

 That the large black slug occurring in the British Isles is 

 the A. empiricorum, Fer., there can be but little doubt. Pollonera, 

 the principal authority on the Arionidez, considers it specifically 

 distinct from A. ater, L. Young specimens are often mistaken for 

 A. subfuscns and A. lusitanicus. Scharff (35) has pointed out that if 

 adult specimens be tapped on the head, they invariably draw them- 

 selves together and arch the body, and if again tapped, the specimen 

 assumes a peculiar swaying movement from side to side. I have also 

 noticed this arched position in A. lusitanicus, A. circumscriptus, and 

 A. inter niedius. 



Anatomy.* — There are two vestibules, an upper and a lower one, 

 into the lower portion of the former the receptaculum seminis and 

 sperm duct ( = Patronstrecke of Simroth) open, the free oviduct opens 

 into the upper portion of this vestibule. The vas deferens is long, but 

 shows no distinct marking between the upper and lower portions, viz. 

 the vas deferens and sperm duct. The retractor muscles are attached 

 to the upper portion of the oviduct, and also to the duct of the 

 receptaculum. The hermaphrodite gland is of a purple brown 

 colour, but subject to much variation ; the duct is convoluted and 

 comparatively long. Scharff (35, p. 539) mentions a variety in which 

 the retractor muscles are attached much lower down the oviduct. 

 This is, I think, likely to be A. lusitanicus, as I have found this to be 

 the case in what specimens I have examined of that species. 



Reproduction. — The eggs are deposited from June to August, 

 and average from 40 to 50 in number. Young specimens show 



Dr. Scharff has so recently described and figured the reproductive organs of most of the 

 forms here mentioned, that I have only given the principal points. 



