1 922. No. 5. ARIOMDAE OF NORWAY. 49 



little greater, than the distance from the outer, anterior corner of the basal 

 plate to the most anterior point of the lateral cusp. 



Reproductive organs (hg. 46) in the Norwegian stock are rather 

 different from those in other countries. While the oviduct (o.) is always of 

 equal breadth and very short (shorter than vas deferens + epiphallusi, the 

 cpiplialliis Up.) of Norwegian specimens is stouter and with a more marked 

 transition from vas deferens [v. d.) than in foreign stocks. The receptaculion 

 (rec.) generality has an oval bladder, a little flattened from both sides, the 

 stalk in full grown Norwegian specimens being shorter than in the stocks 

 of other countries, but in all cases with a basal enlargement. 



All the Norwegian specimens examined have a powerfully developed 

 genital retractor iretr.), shaped like a 

 glossy ribbon of equal breadth, dividing 



into three branches: a slender one x r^-^J^^ . 3 



(/ in the figure) to the oviduct, where /^*^«^ ^.^"^l^ /y^ ' <' 



its point of insertion varies from a 

 little above the middle and downwards, 

 a second one for the stalk of the re- 

 ceptaculum, and a third ij) parallel to 

 the oviduct and inserting on the atrium 

 at the base of the epiphallus. 



The genital atriimi iatr.) as usual 

 is flattened in 3'ounger individuals, 

 presenting almost rectangular outlines ; Fig. 46. Lower parts of the reproductive 



such are as a rule the figures of the organs of ^non intermedius, Til. 



forms in other countries. The Nor- «'''• atrium genitale, ep. epiphallus, o. oviduct, 



, o.-sp.-d. ovispermatoduct, rec. receptaculum, 



wegian specimens, nowever, when lull ,.,,^,.. retractor, v. d. vas deferens. 



grown have a shorter, more globular 



atrium. Orificiuui genitale as stated in the previous section, in the Norwegian 

 stock is situated in the prolongation of the split to the respiratory aperture, 

 not anteriorly. The spcnuatoplicre has never been seen. 



Variation. The species is not remarkable for its variation of external 

 characters. Norway for instance only possesses a single form. All the more 

 interesting therefore are the anatomical peculiarities mentioned above, in 

 several respects separating the Norwegian stock from others. However, 1 

 do not consider it advisable to designate it as a distinct variety, owing to 

 following considerations. First, because all species of this genus vary 

 to an extent that often make possible the finding of connecting shapes 

 when these are sought for, especially in respect of the reproductive organs ; 

 and the previously quoted statement of Simroth (p. 47, foot-note) even 

 indicates the existence of transitional forms. Secondly, in such a group as 

 this I think it is best to avoid varieties based chiefly on internal characters, 

 if other arguments tend to support that point of view. 



Vid.-Selsk. Skr. I. M.-N. Kl. 1922. No. 5. 4 



