372 Developmental History of Infusorial, Animal Life. 



more and more of the fluid portions of the protoplasm, and then 

 divides into two parts, perfectly symmetrical ; these two quickly 

 divide into four, eight, or sixteen, and so go on multiplying until 

 a number of cells is produced, each cell being attached to its 

 fellow by its wall, but capable of a separate existence. By 

 this process of subdivision, a single cell of Protococcus nivalis 

 (Red snow plant) has been known to redden in a single night 

 vast tracts of snow, and the Bovista giganteum is estimated to 

 produce in one hour no less than four thousand millions of 

 cells. Ehrenberg computed the increase of the infusorial 

 animalcule, Paramecium, at two hundred and sixty-eight 

 millions in a mouth. This simple mode of reproduction is 

 certainly identical with that of growth of both plants and 

 animals of a higher type. 



If we ascend a step we reach the second form of repro- 

 duction, namely, the union of two similar cells, termed by 

 botanists " conjugation." This consists in the coalescence 

 of two similar cells to form a new starting point from which 

 multiplication may proceed. Instead of two cells in the 

 same filament we may have two cells in contiguous filaments 

 coalescing, but in each case it is the union of two similar cells. 

 From the fission of one cell into two, and the conjugation of 

 two similar cells, we pass to the third mode of reproduction, 

 namely, generation by ova, or the union of two dissimilar cells, 

 and for the production of the more complex organisms, the 

 union of germ with sperm-cells is indispensable. 



By these several separate modes of reproduction we must 

 admit that there is nothing more marvellous in an animalcule 

 producing several millions of its kind, than in a plant con- 

 structed by as many cells, each produced by a process identical 

 in every way. In the development of the tissues of the animal 

 body, the newly-formed cells increase by division : and become 

 determined in their growth by the character of the secretion 

 elaborated within the walls of those previously existing. The 

 formation of the more complex animal tissues takes place in 

 the same way as that already noticed in plants, with this dif- 

 ference, that the mother cell contains a nucleus, within which 

 is seen a very minute body called a nucleolus. The nucleus 

 has the power of appropriating, or drawing in, a certain portion 

 of the surrounding material — protoplasm — enlarges, and 

 ultimately divides into two perfect cells. From the aggrega- 

 tion of such cells we have the animal body built up in all its 

 complexity. 



We have thus far traced the development of organic life 

 through some very curious and highly interesting stages, and 

 we have seen that life, in all cases, whether in the highest or 

 lowest forms, depends upon perfection of organization for 



