HOW TO VIEW POLYZOA UNDER THE MICROSCOPE. 411 



a few specimens from the heaps before us, and having 

 placed them in a jar filled with their native element, 

 return to our microscope, further to elucidate their 

 history. 



Whoever wishes to study closely the ceconomy of 

 these exquisitely-constructed organisms, should be 

 furnished with a number of glass troughs (which, 

 with the aid of a little cement, may easily be manu- 

 factured of every variety of shape) ; these should be 

 filled with sea-water, and a branch of the species to 

 be examined placed in each, care being taken to adapt 

 the dimensions of the trough to the thickness of the 

 specimen ; it being very desirable that no more water 

 should intervene between the latter and the sides of 

 the glass than is just sufficient for the purpose. The 

 polyps, which always contract the instant that they 

 are disturbed, will soon expand themselves, in which 

 state many may be seen with the naked eye, and a 

 very cursory glance under the microscope will then 

 show which are the best adapted for observation*. 



* A very beautiful Bryozoon is generally to be met with, 

 spreading out in patches of variable size upon the exterior of 

 mussel-shells ; and as this is procurable in a living state with 

 the utmost facility upon any coast where mussels are abun- 

 dant, it will always be at the disposal of any one interested 

 in the study of these elegant beings, more especially as portions 

 of it can easily be detached from the shells whereon they grow, 

 and, being transferred to a watch-glass, attach themselves to 

 their new support, in which condition they may be readily pre- 

 served in a vessel of sea- water. Nothing can be more instructive 

 than the examination of specimens so circumstanced : all the 

 progress of the embryos and cells may be admirably seen, and 

 their development watched from day to day in the most satis- 

 factory manner. 



T2 



