1892.] NEW-YORK MICROSCOPICAL SOCIETY. 19 



nucleus, by enabling them to resolve it into component parts, and 

 to show that within the so-called nucleus a still deeper nucleus 

 exists, and another within this, and so on down, until the powers 

 of the lens are exhausted and the observer can discern at last 

 only a "germinal spot," or point, where somehow, but he knows 

 not how, vital energy emerges or at least manifests itself. 



Further than all this, it has been discovered that numerous or- 

 ganisms exist, in which it is impossible to make out anything at 

 all corresponding to this specialized region; and so the sweeping 

 generalizations which were not long ago accepted, as to the abso- 

 lute necessity of a nucleus to every living unit,, have been com- 

 pletely discredited. Still, a great deal of attention is bestowed 

 upon it in such organisms as do possess it, because in such cases 

 it is evidently the seat of greatest vital activity. 



In the diatoms, the first indication we have that self-division is 

 about to take place is the appearance of a sort of uneasiness 

 within the nucleus and the formation of a constriction about the 

 middle of the endochrome. This is at the beginning a mere in- 

 dentation of the outline, but it gradually deepens and deepens un- 

 til it finally results in the cleaving of the endochrome in twain. 

 It is one of the most impressive sights a man can witness, — this 

 kneading and moulding of the primal matter of a living organism 

 by an invisible agency, under whose mysterious excitement it 

 trembles and surges and at last rends itself apart. One can 

 hardly hope to come nearer than this to the actual first cause of 

 the organic woild. 



Having once seen this manifestation of efficient energy within 

 the diatom-shell, we shall not much wonder that the free frustules 

 move from place to place. We may, however, entertain a lively 

 curiosity as to the direct means by which their locomotion is ac- 

 complished, although, in the present state of knowledge, I am 

 sorry to say, that curiosity cannot be satisfied. 



Amongst the lowest known living things two modes of locomo- 

 tion prevail. When the organism consists of a wholly soft and 

 mobile material, as is the case with the amoebae and many vege- 

 table spores, its progression is a form of slow creeping by means 

 of extemporized limbs, or pseudopodia, which are projected as 

 wanted and withdrawn into the general mass after they have once 

 been used. When the creature is of a firmer structure, with an 



