73 



and living powers of the organism developed from the pri- 

 mary germ-cell and germ-mass. It is consequently longest 

 retained and furthest transmitted in the vegetable king- 

 dom; the zoophytes manifest it in the next degree of 

 force ; and the power of retained germ-cells to develope a 

 germ-mass and embryo by the remnant of spermatic virtue 

 which they inherited, is finally lost, according to our actual 

 knowledge, in the class of Insects, and in the lower Mol- 

 lusca. It is interesting, however, to observe this power 

 energising, as it fades, in the reproduction of parts, e. g. the 

 limbs of the lobster, when it is no longer capable of deve- 

 loping a whole. 



The secondary circumstances attending such develop- 

 ment of a germ-cell retained unaltered in the body, differ 

 from those which attend the development of an ovum, and 

 vary from one another as much as the accessory circum- 

 stances in the development of an ovum vary. An ovum is 

 essentially a nucleated cell called the ' germinal vesicle/ 

 with a granular fluid called the e germ-yelk ' in an envelope : 

 it may contain a supplementary nutrient vitelline mass, 

 properly called yelk, or a yelk with chalazas and a calcareous 

 shell, or a nidamental case and appendages of various 

 kinds, &c., but the essential part is the germinal vesicle, 

 and this cell must be impregnated. The ovaria and the 

 conduits for the conveyance of the ovum outwards are 

 superadded and accessory parts in the business of gene- 

 ration. An impregnated germ-cell imparts its spermatic 

 power to its cell-offspring ; but when these perish, or when 

 the power is exhausted by a long descent, it must be re- 

 newed by fresh impregnation. But Nature is economical ; 

 and so long as sufficient power is retained by the progeny 

 of the primary impregnated vesicle, individuals are de- 

 veloped from that progeny without the recurrence of the 

 impregnating act. 



The germinal vesicle is the essential part of an ovum. 



An impregnated germ-cell is essential to the development 



