MERISMOPCEDIA VENTRICULI. 125 



rendered colourless by the addition of cold sulphuric acid,- When 

 sulphuric acid alone is added, they become reddish or brownish 

 from carbonization. According to Hasse, they become brown 

 when first treated with cold sulphuric acid, and afterwards with 

 iodine. They contract somewhat in alcohol, and are not destroyed 

 even by heat, nitric acid, or the caustic alkalies, but their cellular 

 structure gives way. When pressed between two pieces of glass, 

 they give, according to Lebert, a sandy feeling. Towards 

 reagents they behave as the Diatomacese, on account of which 

 Lebert attributed to them a siliceous covering. But when treated 

 with muriatic acid, and burned, they yield an ash in which the 

 form of Sarcina can no longer be discovered. They are not 

 destroyed by putrefaction coming on in the fluids in which they 

 are contained. Their structure is very simple; they adhere 

 together sometimes merely through contact, and sometimes 

 through a mucilaginous interstitial mass, which swells up in 

 solutions of the alkalies. The cells measure about 0'008-10 mm., 

 and exhibit under the lower powers of the microscope, cubical 

 blunt edges, but under higher powers the edges are sinuous. 

 With lower powers these edges again appear pointed, but with 

 higher powers they are rounded at the corners. They have in 

 the middle of the surface a slight depression. From this central 

 depression there proceed four linear depressions or furrows, from 

 which originate four roundish projections, which, although they 

 are not to be compared with the corresponding formations in 

 Diatomacece, have nevertheless been named " frustula " by Goodsir. 

 The cells lie generally four, eight, twelve, sixteen, twenty-four, 

 &c., together. Through pressure, they break away, and form 

 smaller masses, resembling the parent-cells, and should they pre- 

 sent a kind of envelope, it arises from their coming in contact 

 with the digesting food or mucus. 



Every cell, according to Robin, is either composed of an 

 homogeneous mass, free from nuclei, or more frequently of the 

 same mass with four or two or three nuclei. Both kinds of cells 

 are to be seen near one another, according to the observations of 

 Hasse, Kolliker, Miiller, Simon, Robin, and Lebert. Robin 

 thinks that those who have not seen these nuclei at all, must 

 have accidentally missed them, or used magnifying powers under 

 600 diameters. These nuclei, which are from 2 to 4000th, seldom 

 the 6000th of a millimeter in diameter, are cubical, elongated 



