18 PKOTOZOA [CH. 



fact draining the protoplasm and forming a drop. This drop swells 

 until it, so to speak, bursts the covering of protoplasm separating it 

 from the outside water ; the space it occupies then collapses, but 

 as soon as the fluid has escaped the rent in the protoplasm joins 

 up again, and as the excretory process continues the drop of fluid 

 again accumulates. 



The other object which we may perceive is the nucleus. This 

 is a spherical body consisting apparently of the same 

 kind of material as the endoplasm, only slightly denser 

 (1, Fig. 1). If we, however, kill the animal by running in some iodine 

 under the coverslip, the nucleus stands out at once in contrast to the 

 rest of the protoplasm by its property of taking up more iodine and 

 appearing stained a much deeper colour, and this happens in the 

 case of any Amoeba, whether we have been able to see the nucleus 

 whilst it was living or not. Close examination by means of high 

 powers reveals the fact that only part of the nucleus is concerned 

 in taking up stain. This part which is called chroma tin in 

 Amoeba usually takes the form of a clump or mass which is bathed 

 in a fluid, the nuclear sap, contained within a membrane, the 

 nuclear wall. Chromatin contains phosphorus in combination with 

 a peculiar compound known as nucleic acid. The material contained 

 in the nucleus is an essential part of the body : when an Amoeba is 

 deprived of it, metabolism within the protoplasm slackens and finally 

 stops. Nearly all living things, animals or plants, possess one or 

 more nuclei, though in some rare cases the essential tiuclear material 

 is dispersed throughout the protoplasm. The bigger the plant or 

 animal, the more nuclei it possesses. The so-called "Flowers of 

 Tan" (Mycetozoa), which creep over the hides in tan-pits, are 

 some of the few Protozoa which are distinctly visible to the naked 

 eye; they may be compared to gigantic Amoeba with branching 

 pseudopodia, and they have thousands of nuclei. In the case of 

 certain Protozoa it has been proved that if the animal be broken in 

 pieces, those bits which contain a nucleus can repair themselves and 

 continue to live, and eventually grow up to form an animal like the 

 one of which they are fragments ; but those bits which contain no 

 nucleus, though they continue to live for a short time, have no 

 power of feeding themselves nor of growth. On the other hand if 

 the nucleus be freed from protoplasm it dies ; life depends on the 

 mutual reactions of protoplasm and nucleus. 



The reproduction of Amoeba ordinarily takes place by the simplest 

 conceivable process ; the animal divides itself into two. This 



