VARYING PROPORTION OF BIOPLASM IN THE "CELL." 71 



it. The young cell seems to consist almost entirely of 

 this living material — a fact well observed in a specimen 

 of cuticle from the young frog, which may be contrasted 

 with more advanced cuticle from the same animal. In 

 the mature cells of the fully formed cuticle only a 

 small mass of bioplasm (usually termed the nucleus) 

 remains. 



106. Varjing proportion of bioplasm in tlie " Cell." 

 — In the fully formed fat cell there is so little bioplasm 

 left that it may easily be overlooked. In disease, on 

 the other hand, the bioplasm may increase to three or 

 four times its ordinary amount, when it becomes a 

 very striking object. The ovum at an early period of 

 its development is but a naked mass of bioplasm, with- 

 out a cell wall, but having a new centre and often 

 numerous centres (known as gerrainal spots or nuclei) 

 embedded in it around these, a capsule or cell wall is 

 ultimately formed. 



109. Formation of the " CeU." — The mode of for- 

 mation of the cell, or elemental unit, as well as the 

 origin from it of other units, is well illustrated in the 

 formation of the ovum. The ceils constituting the 

 tissue of the ovary of the common stickleback are 

 very easily demonstrated, and amongst them are 

 seen true ova at a very early period of development. 

 The youngest of these ova differs but little from the 

 " cells" amongst which it lies. It is, m fact, but one 

 of these which has advanced in development beyond 

 the rest. Small but complete ova may be seen with 

 their bioplasm, or living matter, here called germinal 

 vesicle, surrounded by the yolk which consists of 

 formed matter. In the germinal matter are seen 

 numerous germinal spots, which are new living 

 centres of growth originating in living matter. In 

 these are new centres, and in these last, others would 

 have appeared at a later period. The growth of an 

 elemental unit always takes place from within, so 

 that the surface is always the oldest portion. The 



