8 COLLINGE : OBSERVATIONS ON SPECIES OF ARION. 



Its lower portion is characterised by a swelling which dilates 

 into a globose sac (PJ. II., Fig. i, f.ov.), and then is continued 

 as a tube much narrower than in either A. riifiis, L., or A. cmpii'i- 

 corum, Fer, The vas deferens is sharply marked off from the 

 sperm-duct, and is much shorter than in either of the two above- 

 mentioned species. The free-oviduct is a very short, wide tube, 

 little more than half the length of that organ in A. nifiis or 

 A. empiricoriim, and is characterised b}' a large terminal swelling 

 (PI. II, Fig. i). The receptaculum seniinis is pyriform in 

 shape, its duct is short, and widens out at its juncture with the 

 vestibule. The retractor muscle is attached to the duct immedi- 

 ately below the expanded head, and joins that attached to the 

 upper portion of the free-oviduct. 



2. Arion rufus, Linne, 1758. (PI. II, Fig. 2.) 



There are two very distinct vestibules, the upper one being 

 the larger. The sperm-duct shows a series of constrictions and 

 usually''-' bends in the form of the letter L reversed, pass- 

 ing gradually into the vas deferens, a long, thin tube (PI. II., 

 Fig. 2). Sometimes, however, the sperm-duct and vas deferens 

 are sharply marked off from each other. The free-oviduct is a 

 moderately long tube of equal breadth throughout. Tiie recep- 

 taculum seminis is large and ovoid in form, its duct is mucli 

 longer than in A. rt/^r, and about twice the length of that in 

 A. cmpiriconim or A. liisitanicus. The retractor muscles are very 

 similar to those in A. atcr. 



3. Arion empiricorum, Fer., 1819. (PI. II., Fig. 3). 



This is what is termed A. atcr by British authors. There 

 are two vestibules, the lower one being very short and the upper 

 one large and wide, considerably larger than in A . ater. The 

 sperm-duct is a large, wide tube ; it exhibits no constrictions, 

 and makes a sharp turn at the point where the vas deferens 

 commences (Pi. II., Fig. 3). The free oviduct is a long, wide 

 tube with its terminal portion expanded and forming part of the 

 upper vestibule ; unlike A. atcr, it is not sharply constricted from 

 the lower vestibule. The receptaculum seminis consists of a 

 short, elongated sac and a very short duct (PI. II., Fig. 3, r.d.). 

 The duct is not more than half the length of that found in A. ater 

 or A . ritfus, but more nearly approaches the condition which 



* In all the specimens I have examined this feature has been present. 



