82 



QUEKETTS LECTURES ON HISTOLOGY. 



granules are Jth of an inch in diameter, one of them, sliown in section at 

 c, is magnified 12 diameters, and the concentric laminae of which it is 

 composed are well displayed. 



" In Germany there is an Oolite in which the granules are nearly as 

 large as they are in the Pisolite, but the concentric laminated arrange- 

 ment, as shown at D, and the presence of a central nucleus, are more 

 strongly marked ; the rocK supporting the Britannia bridge is a firm 

 Oolite, in which the granules are remarkably small, those represented by 

 B being magnified 40 diameters. The specimens just described are all 

 very compact, the granules being firmly cemented together by the cal- 

 careous material forming the matrix : it sometimes happens, however, in 

 oolitic districts, that the granules are separated from the matrix, and the 

 soil will be seen to be in a great measure made up of them. This is 

 especially the case in the neighbourhood of Bath ; the soil of High Barrow 

 Hill, I found to be so rich in oolitic granules, that when turned up by the 

 plough, it appeared as if thickly sown with minute yellow seeds." 



Fig. 52. 



A, Portion of oolite tenned Roe-stone or Pisolite, b, Granules from Britannia rock, magnified 

 40 diameters, c. Granule of Pisolite magnified 12 diameters, d, Granule of Oolite from 

 Germany, magnified 20 diameters. 



After the examination of the Nummulites, &c., we come to 

 the great group of Zoophytes. These occupy several lectures, 

 and contain many valuable observations. The structure of 

 the skeleton of the Echinodermata is then gone into very 

 carefully. From this part of the work we extract the following 

 passage on the very curious bodies called Pedicellarieae : — 



" We now come to other organs found upon the external surface of 

 some of the Echinodermata, and these are the curious bodies termed 

 Pedicellarice. They were first described by Muller the Danish naturalist, 

 and have been since investigated by Sars, a Norwegian clergyman. 

 Muller believed them to be parasites, whilst Dr. Sharpey and others 

 regard them as parts of the animal, which they undoubtedly are. On 

 most Echini there are three kinds of Pedicellariaj ; being considered as 

 distinct animals, they have been termed Pedicellaria tridens, Pedicellaria 

 triphylla, and Pedicellaria globifera, according to their form ; but what- 

 ever this may be, each consists of a solid part, or skeleton, and a soft 



