242 EXTRACTS AND ABSTRACTS FROM FOREIGN JOURNALS. 



microscopic investigation ; this difficulty, however, is surmounted, if 

 it is macerated for some days or weeks in a solution of caustic potass, 

 especially in a warm place. The alkali removes the greater part of a 

 peculiar brown matter, and leaves the remainder unaltered in form, of a 

 greyish-yellow colour, and cartilaginous consistence, well adapted for 

 examination. 



It will then be found, that the horny case is composed of three 

 laminae, viz., an external and an internal cuticle, and a central fibrous 

 tissue. 



The external epidermis is composed of cells, not very closely attached 

 to each other, about 0.007 0.010 millim. in length, and 0.0050.006 

 millim. in breadth. Their nucleus is a little smaller than the cell itself, 

 and has one or more nucleoli. The internal epidermis is very delicate, 

 and the borders of the cells composing it, are with difficulty made out. 

 They however appear to be more rounded than those of the external 

 epidermis, and by their more close allocation, assume a more or less hexa- 

 hedral form. Their diameter varies from the 0.005 to the 0.010 millim. 

 No nucleus can be distinguished in them ; but instead, a spiculuin pro- 

 jects in an oblique direction from the centre of each cell. 



All these spicula lean in the same direction ; they increase in thick- 

 ness from their point of insertion to the middle, and thence taper to 

 a fine point. Their length is about 0.006 0.008 millim., and their 

 greatest thickness 0.002 0.003 millim. Both the external and in- 

 ternal cuticle are formed of but a single layer of cells. 



The remaining or central part of the shell will now be seen to be 

 composed of a transparent material, marked throughout by numerous 

 dark lines, which are readily ascertained to be formed by several rows 

 of smaller lines parallel to each other, and placed at regular distances. 

 The appearances thus afforded are occasionally very elegant. The mass 

 is readily split into several laminae, the thinnest of which will be found 

 to be made up of little transparent columns, with sharply defined, dark, 

 parallel borders. The diameter of these columns is about the 0.008 

 millim. ; and the above described lines correspond to their borders. 

 These columns or prisms are connected together by the interlacement 

 of delicate filaments, which pass very obliquely from the sides of con- 

 tiguous columns, attaching them to each other. The direction in which 

 these columns are placed forms an angle of 45 with the surface of the 

 laminae which they compose. The number of these laminae is very va- 

 rious ; in some instances as many as sixteen have been counted in the 

 thickness of the horny case. In portions which have not been mace- 

 rated in the alkaline solution, a layer of pigmentary matter, homoge- 

 neous, transparent, is observable between the outer epidermis and the 

 proper horny substance. 



In No. 2 of Miiller's Archives for the present year, is a plate, with 

 figures illustrating the mode of growth and structure of the confervae 

 found growing on frogs, salamanders, &c., by Dr. Hannover. 



