THE CARNIVOROUS SLUGS OP SOUTH AFRICA. 125 



chiefly confined to a thin layer lining the base of the gland 

 and containing the rather large nucleus ; the rest of the 

 interior is filled with mucous secretion, which can be extruded 

 through a narrow pore between the cells of the epidermis. 

 Dr. Plate has sepai'ated the unicellular mucous glands of 

 Testacella^ and Daudebardia" into two classes, according 

 to the nature of this secretion. A similar classification seems 

 applicable to the dermal glands of Apera, for in sections some 

 of the glands are seen to be entirely filled with a vacuolated 

 colourless secretion, while in others the mucus has become 

 concentrated into a compact, deeply stained mass in the centre 

 of the gland. No dermal glands of either kind occur in the 

 foot-sole. In this i-espect Apera resembles Paryphanta,^ 

 and contrasts strongly w4th Testacella* and other forms. 

 Possibly the great development of the pedal gland may have 

 rendered the unicellular glands unnecessary, although in 

 Paryphanta the pedal gland is not much more highly 

 developed than it is in Testacella. 



The minute granules of dark pigment occur in the con- 

 nective tissue between the mucous glands, l)eing chiefly 

 aggregated just beneath the epidermis. Some of the granules 

 are contained in pigment-cells, others appear to be irregularly 

 scattered about, but possibly these may occur inside delicate 

 branches of the pigment-cells. 



Beneath this glandular zone the connective tissue contains 

 blood-vessels, nerves, and numerous muscle-fibres, longi- 

 tudinal, radial, oblique, and circular, the last-mentioned being 

 especially abundant near the inner sui'face of the skin.^ In 

 Apera dimidia there are more muscle-fibres in the foot 

 than in the connective tissue of the back and sides. This 



' Op. cit., p. 530. 



2 Op. cit., pp. 527, 528. 



' Beutler, op. cit., p. 375. 



* Lacaze-Duthiers, H. de, ' Arch. Zool. Exper." (2nd ser.), 1887, vol. v, 

 p. 526. 



* I use the term " skiu " in a wide sense to inchide the whole body- 

 wall, for no sharp line can be drawn separating the subcutaneous tissue 

 with its muscle-fibres from the dermis or cutis vera. 



IBRARYj^i 



