189'7.] MB. W. B. COLLINGE ON EUROPEAN SLUGS. 441 



gations upon two common and widely distributed species, viz., 

 Avion suhfvscus, Drap., and A. hortensis, Ter., which are detailed 

 below. 



Aeion subfuscus, Drap. 



The form and position of the generative organs in this species 

 are illustrated on PL XXIX. fig. 1. Externally the species is one 

 subject to a wide range of variation. I have myself noted some 

 thirty minor coloiu'-variations in addition to the fifty or sixty 

 varieties which have been described by various authors. If this 

 species assumes different colours, markings, &c. in difi:erent districts, 

 which it undoubtedly does, in common with nearly all other 

 species, the value of such as distinctive features is materially 

 lessened, and one is led to ask " Does the form of the generative 

 organs vary to a similar extent ? " 



I have examined 152 lots of this species, each from different 

 localities in various parts of Europe, including in all 751 specimens. 

 All of these were adult and collected during the months of July 

 and August in 1892-3-4-5. Out of this large collection in only 

 four of the lots were variations found, particulars of which are as 

 follows : — 



1. Four specimens collected at Southampton (PI. XXIX. fig. 2). 

 In three specimens the sperm-duct had a globose ring-lilie swelling 

 at its commencement, and the free-oviduct showed the globose 

 form figured. Professor Simroth, who examined a specimen, 

 considered it " a very developed A. subfusciis." 



2. Three specimens from Ireland (PI. XXIX. fig. 3). All slightly 

 smaller and darker than the typical form. All three specimens 

 exhibited a shght difference in the form of the free-oviduct. 



3. Five specimens collected near Knowle, Warwick (PI. XXIX. 

 fig. 4). All belonging to the variety griseus, Cllge. In one speci- 

 men the form of the free-oviduct was somewhat like that in 

 No. 1 (fig. 2), only less globose and more constricted in the middle 

 of the lower portion. 



4. Five specimens collected in Northern Italy (precise locality 

 uncertain). In two specimens both the sperm-duct and free- 

 oviduct differed slightly (PI. XXIX. fig. 5). 



In all the above variations it will be seen, on comparing figures 

 2 to 5 with figure 1, that the distinction between the upper and 

 lower portion of the free-oviduct was very sharply marked. 



Abion' hortensis, Fer. 



Only 83 lots of this species have been examined, each from a 

 different locality, including in all 491 specimens. In 19 specimens 

 the generative organs were found to be immature, thus leaving 

 472. Variations were found in six cases. 



1. Two specimens from Tuxford, Newark (PL XXX. fig. 7). In 

 one the free-oviduct was longer than usual and the sperm-duct 

 more globose. 



2. Ten specimens from Ireland (PL XXX. fig. 8). Three speci- 



