BRYOZOA. 



101 



Introduction. | 



solidity; (2) a piece of water hone one inch thick, a little wider, and four or five 

 inches long; (3) a block of wood (walnut is the best) one inch thick, two inches 

 wide, and four and one-half inches long. The edges of the upper side are rounded to 

 fit the hand, while in the lower side a shallow excavation, one and one-sixteenth 

 inches by three and one-eighth, is made to fit the ordinary glass slip. The excava- 

 tion must be made so that the central portion of the glass slip will bear upon the 

 block, while the ends may have a little play. 



With a strong pair of " wire nippers " a fragment is pinched from the specimen 

 of which sections are desired. This is taken into the fingers and rubbed upon the 

 sandstone until the surface is perfectly flat. This is the most important part of the 

 process, and the greatest care must be exercised to retain (or obtain, as the case may 

 be) the desired angle. This surface is now rubbed smooth upon the hone, when the 

 fragment is ready for mounting. A drop of Canada balsam is placed upon the glass 

 slip, and the ground face of the fragment into it. The slip is now heated (on a 

 heating stage or over a lamp) and the balsam allowed to boil for five or six seconds, 

 when the slip is laid upon a horizontal piece of wood to cool. After it is cold the 

 balsam should be tested, and, if it is not hard and brittle, must be reheated. If of 

 the proper hardness, the block is moistened, the slip placed into the excavation, and 

 the superfluous material rubbed away upon the sandstone. When nearly thin 

 enough it is taken out of the block and finished upon the hone. 



After thoroughly cleaning and drying, the section should be covered with a film 

 of balsam and a thin sheet of glass. Air bubbles, if any are found, should be expelled 

 by gently heating the slide and pressing upon the cover glass. 



Of course it requires a certain amount of experience and time to make good sec- 

 tions, yet even the beginner ought to be able to make from twenty to thirty sections 

 daily, while an expert may increase the number to forty and even fifty. 



For reasons about to be mentioned, these sections must be prepared with a 

 knowledge of certain peculiarities which are common to the Bryozoa, otherwise the 

 sections will be misleading. Take for example any ramose or palmate form, and the 

 student will find that the zoarium of such Bryozoa is composed primarily of two dis- 

 tinct zones, an inner or axial region where the zocecia are tubular, more or less nearly 

 vertical, and with very thin walls ; and an outer or peripheral region composed of 

 the same tubes bent outwards at varying angles in order to reach the surface. In 

 this outer region the zooecia are supposed to have entered the mature condition, and 

 it is here only that such accessory features as the acanthopores and mesopores are 

 developed. 



