24 



to be very active on the microscope stage. This is due to the 

 motion as well as the form being magnified. Its actual rate of 

 movement is something like f of an inch per hour. Still, the 

 apparent great activity of these tiny plants as they glide to and fro 

 unceasingly, pushing and jostling each other, is a very remarkable 

 sight. 



To be able to see the so-called '• striae " of the diatom- 

 valve, it is needful to remove the protoplasm and chlorophyll by 

 acid, or other suitably severe treatment. Then the sculphured 

 lines, of which in P. angulatum there 52,000 to the inch, are 

 faintly visible with a good j of an inch objective. With higher 

 powers the Hues aie seen to be rows of circular markings which 

 have been considered to be elevations by some, depressions by 

 others, but which are undoubtedly apertui'es. (Photomicrographs 

 of P. angulatum, magnified 100, 400, 2,000, and 7,700 diameter, 

 were shown in illustration.) 



From very selfish motives. Amoeba and other Rhizopods, 

 generally seek to associate with Diatoms. This jelly-like, almost 

 structureless animal, Amoeba, although devoid of parts or appen- 

 dages, is very well able to look after its own interests. It glides 

 about among the little plants in an innocent manner, and when it 

 feels huiigiy it imprisons one or two of them within itself, and 

 assimilates whatever is digestible. When it has finished a meal, 

 it moves away, leaving the empty plates, or valves, behind. 



Other Pjhizopods found in company with the Diatoms are 

 Lieberkuchnia, Gromia, and several species of Foraminifira, all 

 of which spread out slimy threads of their body substance, so as 

 to bo able to catch unwary animals and wandering plants much 

 in the same way that spiders catch flies. 



A gradation can be observed in the manner in which the body 

 is hidden from sight by all these simple organisms, except Amoeba, 

 which is content to remain uncovered. 



The first advance in this direction is made by Lieberkuchnia, 

 which forms a temporary covering by merely holding mud 

 particles over and around any portion of itself which otherwise 

 would be exposed to view. This ambush is cast away, renewed, 

 or altered as circumstances may determine. 



Gromia is much larger than the preceeding, being about 

 g^^ of an inch in its longest diameter, and it improves upon the 

 habits of its less enlightened relative by felting particles together 

 so as to form a permanent wrapping itself. 



Some specimens vary fro ii the type in having a zone of oval 

 apertures around the usual single circular one. These do not 



