240 THE AMEHICAN MONTHLY [Aug, 



smallest rotifers. They sometimes actively clear up a 

 space around themselves five or more times the width of 

 their own diameter, when the granules are seen to be 

 projected with great rapidity. A one-sixth lens, having 

 little penetration relatively, is in this case best adapted 

 to showing the phases of the pseudopodial flow, rather 

 than the apparent attraction or repulsion of the carbon 

 granules. This, however, can be readily witnessed with 

 a one-half inch lens as already described. In addition 

 to the active and passive ends of the diatoms while in 

 motion, there are other effects to be noted. Such are 

 the peripheral wave motion or phosphorescent-like un- 

 dulations of the exoplasm 'in contact with the siliceous 

 sides of the frustule. When the sigmoid lines of gran- 

 ules are not visible, the play of the epidermic layers in 

 the vicinity of the nodules (which are good tests for good 

 eyesight), may be readily seen. Around these points 

 are well shown the minute phosphorescent flashes of 

 light when the emerald green glass is used as a stage 

 screen to cut off the glare and red rays of the light. 



A hypothetical conception of the tissues which control 

 and support the sigmoid lines of granules is as follows. 

 In the valular faces of the Naviculse there is a slit-like 

 line connecting the terminal nodules with the median 

 nodular cavities of the Navicula. In this nodular cavity 

 can always be seen the two dots indicating the extrem- 

 ities of the cleft of the raphe. Through these nodular 

 dots, together with the cleft along the raphe, there is 

 extruded at times an alate or ring-like process of 

 protoplasm from the internal portion of the frustule. 

 Its contractile and extensile phases may be controlled by 

 some vital power resident in and appropriate to the 

 functional power of the nucleus. This is situated in the 

 endoplasm between the nodular expansions the same as 

 in other nucleated organisms. When in action the alate 

 protoplasmic appendages seem to possess an equivalent 



