ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 549 



short arms differ from those uf)ou the long arms, the main difference 

 being that, while the former are furnished with muscles directly- 

 continuous with those of the peduncle, the latter contain no muscles 

 at all, but only a mass of parenchymatous tissue between the two 

 epithelial layers. 



Histology of the Digestive System of Helix.* — From a study of 

 H. pomatia var. grandis, Dr. F. Bonardi, who has made frequent use 

 of double-staining methods, finds five distinct layers in the wall of 

 the buccal mass, viz. (1) The outermost, of connective tissue, 

 consisting of a fibrillated basis and of nuclei, and of a few distinct 

 cells, which often contain calcareous concretions and refractive fatty 

 globules ; and next to it (2) muscular, in two layers, the outer longi- 

 tudinal, the inner circular. They form an exception to the characters 

 of the muscles in this animal, in often being in appearance trans- 

 versely striated ; this is, however, probably only owing to a j)ecu- 

 liarity in the arrangement of the fibres within the sarcolemma. 



(3) Connective tissue, a continuation of the tunica connectiva of the 

 other parts of the digestive system, containing granular cells, 



(4) Cylindrical epithelium, the cells very long ; over the prominence 

 described by Semper in the upper and lower parts of the buccal 

 cavity it is ciliated. (5) Cuticula, of considerable thickness ; it is 

 stratified in a longitudinal direction, and some large strife placed 

 perpendicularly to the surface of the epithelium perhaps represent 

 tine canals. The tongue consists chiefly of a muscular mass ; this 

 includes three distinct muscles, two of which are symmetrical and 

 posteriorly separate, so as to embrace the lingual papilla ; the third 

 lies transversely below and unites them in the median and hinder 

 parts of the tongue. All are isolated by connective tissue. The 

 surface of the tongue is divided up by two sets of grooves into quad- 

 rangular spaces, on vv^hich are placed a large number of whitish 

 pyriforra papillae. The lingual papilla (at the base of the tongue) is 

 covered by connective tissue, beneath which lies a layer of circular 

 muscular fibres, covering a very distinct tunica connectiva, apparently 

 not hitherto observed, containing oval cells with distinct outlines, 

 imbedded in granular matter. It lies next to the cylindrical epithe- 

 lium of the radula. 



The centre of the papilla consists of a transparent colourless 

 substance, the external parts of which, near the radula, have the 

 structure of connective tissue. The other parts contain fibrils going 

 in various directions. At certain points they are inflated and have 

 nuclei. They make up the " legs of the papilla," and become mingled 

 with the lateral muscles of the tongue. The alimentary canal (viz. 

 the oesophagus to the end of the duodenum) has (1) an external 

 connective coat corresponding to the peritoneum of the higher ani- 

 mals, underlaid by (2) double muscular, and (3) a coimective layer 

 corresponding to the vertebrate mucosa, and (4) an 02)itholial layer 

 covered V>y a cuticula. The muscular fibres are not striated; those 

 of the one layer are longitudinal, of the other transverse, some 



• Atti Accad. Soi. Torino, xix. (1883) pp. 33-46 (1 pi.). 



