PROD I CTION OF FORMED MA TERIAL. 2 1 9 



the elemental unit, as well as the origin from it of other 

 units, is well illustrated in the formation of the ovum. In 

 PI. IV, fig. i, the "cells" constituting the tissue of the 

 ovary of the Common Stickleback are represented, and 

 amongst them are seen true ova at a very early period of 

 development. The youngest of these differs but little from 

 the cells constituting the ovarian organ, amongst which it 

 lies. It is, in fact, but one of these which has advanced in 

 development beyond the rest. In Fig. 2, a small but com- 

 plete ovum is seen with its bioplasm, or living matter, here 

 called germinal vesicle, surrounded by the yolk which con- 

 sists of formed matter. In the bioplasm are seen numerous 

 germinal spots, which are in fact, new living centres of growth 

 which have originated in living matter. In these, again, are 

 yet other new centres, Figs. 3, 4, 5, and in these last, others 

 would have appeared at a later period. In all cases the 

 lifeless nutrient material must pass into the very centre of 

 the living particles, and there, in some way at present un- 

 known to us and beyond conception, the peculiar vital 

 properties are communicated to it. 



On the Prodiiction of the Formed Material of Tis 'sues from 

 Bioplasm. The processes of growth and increase of bio- 

 plasm and tissue, as they occur in the tissues of all fully- 

 formed living beings, may be well studied in the simple 

 tissue (cuticle) which forms the external covering of the 

 body, and which is prolonged in a modified form (epithelium 

 of mucous membranes) into the internal cavities. If a 

 thin section be made perpendicularly through this cuticular 

 tissue down to the tissue upon which it rests, and which 

 contains the nerves and blood-vessels, the appearances 

 represented in PI. V, fig. i, will be observed. 



