222 MORPHOLOGY OF INVERTEBRATE TYPES 



or nephrostoma. The genital opening also is situated on the right 

 side, in front of the mantle, about halfway between the latter 

 and the anterior edge of the animal and about halfway between 

 the right margin of the foot and the mid-dorsal line. Limax is a 

 hermaphrodite, but the reproductive cells do not ripen simulta- 

 neously, so that the creature functions either as male or as female 

 at one time. During its female state, the genital opening serves 

 as a vulva; during the male state, the penis is protruded through 

 it and appears as a cylindrical body with a triangular terminal 

 fin. The position of the pneumostoma and of the genital opening 

 is characteristic of the genus. 



Integument. The integument of Limax is composed of 

 a single layer of epithelium and of a dermis. The cuticle produced 

 by the epithelial cells is very thin and presents numerous pores. 

 Large gland cells originally belonging to the epithelial layer form 

 a sub-epithelial layer. Between the gland cells under the epithe- 

 lium are pigment cells which belong already to the dermis. The 

 most important elements of the latter are connective cells and 

 muscle fibres. An especially large caudal gland is located in the 

 integument near the posterior end of the body. The muscular 

 fibres are especially well developed in the foot. 



Mantle. The shield of Limax is a true mantle, i. e., a 

 fold of the integument, although in this case considerably less 

 developed than in that of the lamellibranch Venus. The epithe- 

 lial layer secretes a shell which is thin and rudimentary. More- 

 over, it is internal in position, lying under the epithelium, and is 

 apparently without function, since in other genera it is com- 

 pletely wanting. The pneumostoma, the position of which has 

 been described above, leads into the mantle cavity which is 

 homologous with the mantle cavity of other gasteropods, al- 

 though Limax is an air-breathing slug. 



Muscular system. The system of muscular fibres in the 

 foot serves all purposes of locomotion and there are few individ- 

 ualized muscles in Limax. The muscles belonging to other sys- 

 tems will be described in their proper places. It suffices here to 



