Biddulphia Mobiliensis. By E. M. Nelson. 159 



and it may be suggested that they are placed there to guard the 

 internal plasma from bacterial attacks. 



The subject is of some interest to microscopy, as these 

 secondaries have only been seen with long-tube Microscopes, and 

 it is very probable that this resolution will never be reached by a 

 short-tube Microscope. 



It has often been asked, Which is the better instrument of the 

 two ? A decisive answer can at once be given to this question. 

 If the instrument is required for the examination of the most 

 minute structures, the long-tube is the better ; but if it is required 

 for other things, such as portability or cheapness, then a short-tube 

 may be preferable. But so long as a Microscope is employed for 

 the highest purpose, such as the revelation of the minute unknown, 

 then a long-tube has no rival. 



The ultimate appeal concerning any very minute structure must 

 go to a long-tube Microscope. 



