156 Microscopical Society. 



Conchifera. He commenced his researches during the spring of 1842, 

 and the first subject for examination was the young cartilaginous lips 

 of the common Garden Snail, Helix aspersa ; subsequently he has 

 directed his attention to the testaceous coverings of numerous spe- 

 cies of adult univalve and bivalve shells. The general results of the 

 examination of the lips of the Garden Snail were as follows : — The 

 newly-formed lip was found to consist of a thin yellow-coloured 

 horny substance, with a number of minute globular vesicles (incipient 

 cytoblasts and cells) in various stages of development, with a nucleus 

 very visible by means of a power of 600 linear in the greater number 

 of them ; these cells were most numerous on the inner side of the 

 lip, or that part in contact with the shell ; the young shells were trans- 

 parent, but in the neighbourhood of these there may be seen aggre- 

 gated together small patches of a deep yellow colour, which appeared 

 as centres of ossification. Besides these other cytoblasts occur, which 

 are developed in the form of tessellated cellular striicture, which ulti- 

 mately form a minute vascular tissue which is imbedded in bands cor- 

 responding in their direction with the lines of growth of the shell ; as 

 these tissues approached maturity, the periostracum advancing from 

 the old lip covers them and binds the whole firmly together. The 

 examination by transmitted light of thin sections of univalve shells, 

 made by the lapidary, afforded but little information of their true 

 structure ; but fractured surfaces at right angles to the outer and 

 inner planes of the shell, and either parallel or at right angles to the 

 lines of growth, when examined by the Lieberkuhn, exhibited three 

 distinct strata uniform in the nature of their structure but alterna- 

 ting in the mode of their disposition : each structure is formed of in- 

 numerable plates composed of elongated prismatic cellular structure, 

 each plate consisting of a single series of cells parallel to each other. 

 The structure of bivalve shells is rather more complicated than that 

 of univalves : the interior surface of some specimens exhibits a thin 

 stratum of columnar basaltiform cells at right angles to the natural 

 surfaces of the shell, whilst the upper is dense, uniform, and composed 

 of numerous thin laminae parallel to the natural planes of the shell ; 

 in other species the inner surface of about half the substance of the 

 shell is composed of numerous thin calcareous strata, whilst the outer 

 half presents the appearance of numerous basaltiform columnar cells 

 having their planes at right angles to the surface of the shell : several 

 other differences in the arrangement of the cells in other genera 

 were then given. The author went on to describe a minute vascular 

 tissue which embraced some of the elongated prismatic cells and 

 gave them a striated appearance. Minute canals corresponding to 

 the Haversian canals in bone, only much more minute, were also to 

 be seen in some specimens ; the author then alluded to the fact that 

 there must be of necessity some vascular connection between the 

 animal and its shell, although he had at present failed in detecting 

 any. He concluded by describing the mode of reparation of injured 

 parts, which was found to be precisely similar to the formation of 

 the new lip in Helix aspersa, as before described. 



Beautiful figures of the principal structures described accompanied 

 the communication. 



