8 A PRIMER OF BIOLOGY 



tion of a stimulus which we are accustomed to term 

 " sensation," at least we have no means of determin- 

 ing whether sensitivity in plants and in lower animals 

 is accompanied by consciousness or not. 



Again, the organism, plant or animal, is, as obser- 

 vation tells us, one of many of the same kind, type 

 or species. In some cases at the completion of, but 

 in most cases, at some stage in its life-history, the 

 organism makes provision for the continuance of the 

 race by separating off a part of its body capable of 

 giving rise, under suitable conditions, to a new 

 organism of the same type. In some cases, the co- 

 operation of two individuals is necessary for the 

 formation of this unit, in other cases it may be pro- 

 duced by one parent only. The " germ," as we may 

 for the present term- this isolated part, is, in short, 

 either simple in the sense of being a single part, 

 segmented off from one individual, or compound, 

 i.e., the product of the fusion of two parts separated 

 from two individuals or from two different parts of the 

 same individual. In the latter case one of these parts is 

 termed the male element, or sperm, the other the 

 female element, or ovum. As every one knows, organ- 

 isms produced by either of these methods show all the 

 chief characters of their parent or parents, while at 

 the same time exhibiting many, and often consider- 

 able, variations from the parental type. The off- 

 spring inherit the fundamental characters of the parent 

 or parents, but show individual peculiarities or 

 variations of their own. 



Let us now quite briefly consider a couple of 

 illustrations, one taken from the plant, and one from 

 the animal world. 



Growing on the surface of the soil of old flower- 

 pots or in damp situations near farmhouses may 



