36 



!■ KIDI IIJOK OKI. AND. 



M.-N. Kl. 



Fig. 32. Reccptaciilum of 

 Arion circiunscriptus, ^/l . 



rec. the bladder of the re- 

 ceptaculum, reir. retractor. 



'I"h(' genital ntrimn {air.) gives perhaps the most constant character 

 of the species, being long and flat like a ribbon. However, in dissecting 

 it is of some imjiortance to note that its lower side is fixed to the bottom 

 of the body cavity with little fibres, and these being separated, the shape 

 becomes more distinct. In connection with the long 

 atritim there must be seen the anterior position of the 

 genital aperture (orificimn genitale), which is situated 

 in front of the split of the pneumostome in all the 

 Norwegian specimens which have been examined 

 (fig. I ). This character is not without interest, as 

 the anterior position of the genital aperture has been 

 the cause of including some other species in the 

 genus (later on the sub-genus) Ariiiiiciiliis Lessona; 

 as the extra-Norwegian populations of Arion circum- 

 scriptits, however, have always been described as 

 belonging to the normal type, the position of the 

 genital orifice appears to vary in the same species, 

 and accordingly cannot be used even as a specific 

 character, far less as a sub-generic one. It must, 

 however, be pointed out that this character should be examined in other 

 countries. (The full evidence that the group Ariwiculiis should be rejected 

 is to be found under Arion intermedins, p. 46 — 47). 



The spermatophore (fig. 34) was unknown until I happened to find it 

 in the receptaculum of 5 specimens, collected on the 30th of June at Vestre 

 Aker near Kristiania. They 

 measure, contracted: s'A, 

 2V2, 2^/2, 2^/2 and 3 cms. 

 Each receptaculum contains 

 a spermatophore, the effect 

 of which is to produce an 

 unusual length and rigidity 

 (fig. 33). One end of the 

 spermatophore is in the tip 

 of the receptaculum, the other 

 is strongly curved and firmly 

 joined to the wall of the blad- 

 der in a manner that attracts 

 attention even before the re- 

 ceptaculum is opened. 



The fully extended sper- 

 matophore would measure 



about I cm., but in the receptaculum it is bent in two planes perpendicular 

 to each other. It is yellow, transparent, firm and elastic. The end situated 

 at the base of the receptaculum was decomposed. The shape is that of a 



/S^. 



Fig. 33. Receptaculum of Arion circuniscriptits, 

 extended by a spermatophore, '/l 



o. oviduct, rec. the bladder of the receptaculun, 

 retr. retractor. 



