82 C. F. MARSHALL. 



to be the best treatment; or, in some cases, a warm chamber 

 (40° C.) was used. A longer immersion than one or two 

 hours in the formic acid in these cases leads to disintegration 

 of the tissues. In addition to the gold preparations, osmic 

 acid preparations were made in most cases, and compared with 

 those made by the gold method. Osmic acid is well known for 

 its property of fixing the histological elements in their natural 

 state. 



The examination of fresh tissues was in many cases of very 

 little use ; for the cells of the striped muscle of many of the 

 animals investigated are so small that under a high power they 

 barely appear striped, and no network can be seen at all. In 

 these cases it is only by softening the fibre and so swelling it 

 out, and at the same time staining the network, that the latter 

 can be demonstrated ; this is the special action of the method 

 of gold staining. 



It is necessary to mention that the results obtained by the 

 gold method are somewhat uncertain. In some cases the net- 

 work will come out distinctly, but in others, especially when 

 the preparation has been left for a longer time than usual in 

 the acetic acid, the network appears to consist of rows of 

 granules instead of definite lines. This uncertainty was 

 noticed also by Retzius, Gerlach, and Bremer, and is no doubt 

 the cause of the different appearances described by these 

 authors. 



In order to avoid the monotony and interruption of re- 

 peatedly stating the treatment used for the muscle of each 

 animal, the exact method used is given with the description of 

 the figure of each animal in the plates at the end of the paper. 



I shall now take the chief group of the animal kingdom in 

 their zoological order, describing the muscle found in each 

 case. 



