COLLINGE : MYOLOGY OF SOME PULMONATA. 53 



At the very outset of my investigations I soon found, what nearly 

 all workers in other groups have noticed, viz. that the muscles which 

 do not supply either sense or other important organs are subject to 

 great variation in form, size, position, etc. Having noted this, the 

 actual scope of my investigations resolved itself into a comparatively 

 simple series of observations upon the following muscles : — 



1 . The buccal retractor muscle. 



2. The tentacular retractor muscles. 



3. The genital refractor muscles. 



1. The Buccal eeteactor muscle. 



In the genus Arion this muscle arises on the right side of the 

 posterior portion of the mantle ; passing forward it divides into two 

 equal branches, each of which diverges laterally, and is attached to the 

 sides of the buccal cavity. An examination was made of thirty speci- 

 mens from various localities, but no variations were found. 



In Limax this muscle arises in the posterior median portion of the 

 mantle and passes forward, giving off the tentacular retractors. It 

 divides into two branches, as in Arion, only the division is more 

 anterior, each branch passing to the sides of the buccal cavity. 

 Twenty-five specimens were examined, but no variations were found 

 in any. 



A similar series of TTelix aspersa, Miill., were examined, no one of 

 which showed any vai-iation. 



2. The Tentacular eexractob muscles. 



In Arion these muscles arise on the posterior and lateral border of 

 the mantle as two small bundles of fibres, which, passing forward, 

 imite ;• this, however, is not a true union, the two muscles remaining 

 quite distinct. At the anterior border of the mantle they divide 

 again. The inner (inferior) one supplies the lower tentacle, and the 

 outer (superior) the ixpper tentacle. A small inner and dorsal branch 

 is given off fx'om the superior retractor, which joins with a similar but 

 larger one from the inferior retractor, the two passing around and 

 above the mandible on either side. These smaller branches were 

 found in a few cases to vary slightly. 



The tentacular retractors in Limax are the same as in Arion, 

 excepting that they arise as one from the buccal retractor. No 

 variations were found. 



3. The Genital retractor muscles. 



These are a group of muscles supplying the oviduct receptaculum 

 seminis and duct, sperm duct, and penis. The form, position, and 

 branching of these have been carefully noted in a very large series of 

 each of the genera named. 



In Arion numerous variations were found, and one or two of the 

 more important may be mentioned. In one case, an example of 

 A. suhfuscus, the retractor muscle supplying the oviduct had its 

 point of origin 15 millimetres posterior to the mantle ; another, 

 A. empiricorum, had its point of origin much anterior to the position 

 of attachment to the oviduct, and in examples of the same species 



