Miscellaneous. 187 



investigation, the knowledge which we possess about it m\ist still 

 be termed incomplete. This is to a certain extent due to the fact 

 that the majority of tlie treatises dealing with the question belong 

 to a period at which the methods of investigatioia were not suffi- 

 ciently developed, and when, moreover, many questions, the solution 

 of which is to-day a matter of the first importance, were as yet 

 entirely untouched. Eecent writers have satisfactorily filled up a 

 portion of these gaps in the development of the Gastropods, yet 

 many a question — and this applies especially to the Pulmonata — 

 still awaits its solution, I had the opportunity of collecting and 

 examining a rich material of embryos of different terrestrial Pul- 

 monates, and I purpose to give in the following pages a brief account 

 of certain results of my investigations, which are not yet completely 

 concluded, concerning the development of the central nervous siistem. 

 An exhaustive account of the development of this, as well as of the 

 remaining systems of organs, will, however, be reserved for a subse- 

 quent publication, in which my statements, supported by figures, 

 shall be compared with those already to be found in the literature 

 of the subject. 



I investigated the development of the following forms : — Succ'ma 

 piitris, L., Clausilia laminaia, Mont., and a few other species of the 

 same genus; Lbnax cinereo-niger and L. agrestis, L. Excluding a 

 few deviations, the forms mentioned agree well together in their 

 development. The statements in the present paper refer to Limax 

 agrestis and Clausilia laminata. 



The entire central nervous system arises by proliferation of the 

 external epithelium of the body, and is therefore exclusively ectodermal 

 in origin, a fact which agrees with all reliable statements of recent 

 investigators of Gastropod embryology. I preface my account of 

 the origin of the several pairs of ganglia with a short description 

 of the epithelium of an embryo at the corresponding stage of deve- 

 lopment. 



The epithelium of the young and still spherical embryo consists, 

 with the exception of four regions of the body which will be men- 

 tioned forthwith, of lai-ge cubical cells, the protoplasm of which is 

 only very slightly stained by the reagents employed by me (alum- 

 carmine and haimatoxylin). On both sides of the wide oral 

 opening, however, the epithelium is composed of close-packed 

 cylindrical cells, which are considerably smaller and at the same 

 time relatively elongate, and take a deep stain ; these regions of the 

 body therefore appear by condensed light as two oval, subsequently 

 reniform, sharply circumscribed disks, the '■'■ sensory plates." Be- 

 hind the oral region, corresponding to the subsequent ventral sur- 

 face, there extends a roundish area, the cells of which are entirely 

 similar to those of the sensory plates ; this disk of cells soon pro- 

 jects as a blunt cone : it is the earliest rudiment of the foot. Border- 

 ing upon this, and extending on to the dorsal surface, we find a 

 similar circular disk of cells — the rudiment of the mantle, tvith the 

 shell-gland. 



In the course of the further development the whole of the super- 



