Descriptive Biology 95 



the algas may have many or none. In the latter condition, 

 shown by the bacteria and blue-green algaB the nucleus prob- 

 ably consists of numerous granules scattered throughout the 

 cell. 



While the majority of unicellular organisms show a more 

 or less high degree of specialization, there are a few which 

 still remain more nearly in what was undoubtedly the primi- 

 tive condition and which may therefore be regarded as pos- 

 sessing greater possibilities of advance to higher types. Such 

 among animals is the Amoeba, while among plants the most 

 primitive are the Protococcacea'. The minute flagellate forms 

 known by the non-committal term of "monads" are undoubt- 

 edly however very close to the bottom of the ladder of life, 

 and it is quite possible that they represent the starting point 

 for both animals and plants. Whether these primitive forms 

 are very ancient, representing the direct descendants of the 

 original progenitors of living things, or whether they are 

 recent, and represent one of many evolutions of living from 

 lifeless matter is an interesting problem for speculation, but 

 one offering small possibilities of solution with our present 

 knowledge. In view of the great variability of most forms 

 of life the likelihood of any group of organisms persisting with 

 but little change throughout biologic time seems most improb- 

 able. But on the other hand we have no evidence of the 

 origin of living from lifeless matter at the present time, and 

 we know further that some forms of the present day (i. e. 

 Spirifer, one of the Brachiopoda) are indistinguishable save 

 in minor characters from their representatives of the Cam- 

 brian period, which may have lived some four hundred mil- 

 lions of years ago. 



Among both the Protozoa and Protophyta are many species, 

 in which the cells instead of remaining distinct are grouped 

 in colonies. In many of these the association is loose and 

 indefinite, the group increasing in size for an indefinite time 

 and finally breaking up to form other groups. This is espe- 

 cially true of the numerous filamentous algae, but is also true 

 of other algae and Protozoa. In some however notably in the 

 Volvocaceae the size and the number of cells comprised in the 

 colony is more or less definite, foreshadowing the conditions 

 in the many-celled animals and plants. 



Among both unicellular plants and animals reproduction 

 occurs typically by simple cell division. At the time of divi- 

 sion the parent cell loses its identity but does not die, con- 

 tinuing to live in its two descendants. The theoretical 

 possibilities of increase of these microscopic forms are beyond 

 our powers of imagination. According to Professor Morgan, 

 a protozoan Stylonichia "produced in 6Y2 days a mass of 



