184 



GASTROPODA. 



has also included various other fresh-water Pulmonates as well as 

 terrestrial Pulmonates in his comprehensive researches. These latter 

 forms, which had already been studied by Gegenbauk, differ from 

 the aquatic Pulmonates in some points of their development and 

 therefore require separate treatment.* 



The ontogeny of the stylomatophorous terrestrial Pulmonates 

 is characterised by the development of exceedingly large provisional 

 organs, viz., the cephalic and pedal vesicles. These larval organs 

 appear early. At a stage which corresponds somewhat to the 



Fig. 82. — Embryo of Helix pnmatia, ten days old, seen from the side (after Pol), a, 

 anus; ,/', foot; Kbl, cephalic vesicle ; ///, larval heart ; m, month ; md, enteron and 

 digestive gland ; r, radular sac ; sd, shell-gland : un, primitive kidney. 



Trochophore stage, the embryos (<>!' Limax, Avion, Helix, Glausilia) 

 are distinguished by the great swelling of the pre-oral section of the 

 body. At the stage of which we speak, this cephalic vesicle is so 

 large as almost to eclipse the rest of the embryo. At a rather later 

 stage also (Fig. 81), the cephalic vesicle (kbl) is still very large, but 



*[See also the more recent works of Holmes (No. XIII.), Kofoid (No. XIV.), 

 Meissenheimer (No. XVII.), Schmidt (No. XX.) and Wierzk.tski (No. XXVII.), 

 These deal for the most part with the cleavage and cell-lineage. Meissen- 

 heimer's researches on Ziimax, however, are carried further and should be 

 consulted in connection with the development of the Stvlommatophora. — 

 Ed.] 



