276 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



F. moulinsiana, Braunton 



Cothill 

 F. antivertigo, Braunton . 

 F. substriata, Dolgelly 

 F. pygmcBu, Branscombe . 

 F. alpestris, Dolgelly 

 F. pusilla, Dolgelly 

 T. britannica, Branscombe 

 C. edentula, Cotbill . 



Totals .23 .46 



It will be noticed that in three of these species all the specimens 

 examined possess a penis ; in two species none of them do ; while in 

 three species some of the individuals have a penis but the majority 

 are without this organ. No intermediate specimens occurred in which 

 the penis was only partly developed ; it seems to be always either 

 present or entirely absent. In those animals which lack a penis the 

 other organs are fully developed, and spermatozoa are present in 

 the hermaphrodite gland and duct. Moreover, in at least some of 

 these species, as in the case of Acanthinula aculeata and Vallonia 

 costata, specimens with and without a penis may be found together 

 at the same time and in the same locality. 



These facts show that the frequent absence of the male organs in 

 this family of snails can scarcely be due to the immaturity or senility 

 of many of the specimens, or to any influence of the environment ; 

 it would seem more probably to be a mutation caused by some 

 hereditary factor.^ But as this mutation is so common among these 

 snails, it is probable that the absence of a penis does not seriously 

 interfere with the animal's reproductive powers in the case of these 

 minute species. Possibly the spermatozoa pass straight down the 

 oviduct and vagina, which are no broader than the vas deferens 

 and epiphallus of a large snail ; and in copulation the very short 

 distance that they have to travel may render a special intromittent 

 organ unnecessary. On the other hand, it is quite possible that self- 

 fertilization, which evidently occurs occasionally in some of the larger 

 snails and slugs, may be the normal method of reproduction in these 

 genera. The chances of successful copulation would not only be 

 reduced by the limited locomotory powers of such small snails, as 



' ^ The ten species in which this phenomenon is now known to occur belong 

 to four different genera ; nevertheless, they are all orthurethrous forms not 

 distantly related to one another. Collinge has described single abnormal 

 specimens of Arion intermedins Normand and Helix aspersa Miill. with no 

 male organs ; but these are extremely rare abnormalities, and in them the 

 receptaculum seminis is said to be absent, as well as the male ducts {Journ. 

 of Anat. and Physiol., vol. xxvii, 1893, pp. 237, 238). 



