Owen's theory;. 301 



All organisms, plant or animal, originate in a cell. This 

 cell spontaneously divides into two, these two into four, 

 these four into eight, and so on, till, instead of a solitary nu- 

 cleated cell, a mass is present, known as the " germ mass." 

 (Plate VI., figs. 4, 5, 6, 7, 8.) In the Conferva, instead of a 

 mass, a thread of cells has arisen, forming the filament which 

 constitutes the whole plant. In the animal, the cells have 

 not been placed end to end, thread-like, but side to side, and 

 form what is called the " mulberry mass " (fig. 8) ; and a 

 further distinction is to be noted, namely, that each animal 

 cell, as it formed, carried with it a portion of the yolk. From 

 the " germ mass " the animal is evolved. Each cell of this 

 mass is the ofi'spring of the primary germ-cell, reproducing 

 its powers and capacities. As the animal is formed out of 

 this mass, and by means of it (figs. 9, 10), we are forced to 

 the conclusion that the cells have become transformed into 

 tissues. But " not all the progeny of the primary germ-cell 

 are required for the formation of the body in all animals : 

 certain of the derivative germ-cells may remain unchanged, 

 and become included in that body which has been composed 

 of their metamorphosed and diversely combined or confluent 

 brethren : so included, any derivative germ-cell, or the 

 nucleus of such, may commence and repeat the same pro- 

 cesses of growth by imbibition, and of propagation by spon- 

 taneous fission, as those to which itself owed its origin." * 



It is this, according to Owen, which constitutes Partheno- 

 genesis. Some of the cells, instead of being transformed 

 into tissues, remain, imchanged as cells, included in the body, 



* Owen : Paythciiogenesis, p. 5. 



