l886.] NEW-YORK MICROSCOPICAL SOCIETY. 13Y 



myself have seen the epidermal membrane. I simply say that 

 accomplished microscopists aver that they have seen it. Be- 

 sides, in science we often know more than we have learned 

 through the medium of the eye. I have never seen, with the 

 physical eye, the enclosing pellicle that sustains the sphericity 

 of the dewdrop which enjewels the petals of the summer rose. 

 Yet to the eye of reason it is visible. Then, is the dewdrop a 

 cell ? No, because, though the seat of the play of wonderful 

 forces, it is not organic at all. It is without structure. Except 

 that it is a fluid, it is like a pure quartz crystal, homogeneous 

 throughout. Even the encasing pellicle differs from the en- 

 closed contents only in this, that the molecules of water which 

 compose it adhere to one another more closely and with greater 

 tenacity than do the molecules within. As to the diatom, the 

 film entirely invests each half of the little box, while within, 

 according to a recent view, are two silicate layers, the one next 

 to the film containing the pattern of the sculpture of the little 

 box. 



So, we have simplified our cell into a tiny box. Indeed, years 

 ago, Prof. H. L. Smith described the diatom as a siliceous box 

 in two halves ; in some, such as the Finnularia, one part slipping 

 over the other, as the upper half of a pill box slips over the 

 lower half ; in others, the two halves simply touching, as in 

 Fragillaria. As to the parts of this tiny box : The part exposed 

 to view when we are looking at the line where the two valves 

 touch, is the front view, just as when we look at the keyhole of 

 a trunk we see the front of the trunk. But the trunk has a 

 back, as well as a front ; whereas, the diatom, somewhat anoma- 

 lously, has its front all around. What we call the top and the 

 bottom of the trunk, in the diatom we call the sides. It is ob- 

 servable, too, that the aspects of the two sides frequently differ. 



Third. Let us now look inside this diatom casket, and, if 

 possible, inspect its contents. It contains a glairy substance 

 which we will call protoplasm. Much of this has passed 

 through its differentiation. Some of it, however, is still but 

 little more than unaltered life-stuff. The larger part is a yellow- 

 ish-brown viscid matter. If we take a leaf from any ordinary 

 plant of flowering rank, say a Pelargonium, we observe that the 

 soft parts of the leaf are green, and this green matter the bot- 

 anists call chlorophyl. Of this the uni-celled algse, such as the 



