THE GERM-CELLS 



89 



rise by regeneration to a complete body. The distinction between 

 somatic and germ-cells is an expression of the physiological division 

 of labour ; and while it is no doubt the most fundamental and impor- 

 tant differentiation in the multicellular body, it is nevertheless to be 

 regarded as differing only in degree, not in kind, from the distinctions 

 between the various kinds of somatic cells. 



In the lowest multicellular forms, such as Volvox (Fig. 41), the 

 differentiation appears in a very clear form. Here the body consists 

 of a hollow sphere the walls of which consist of two kinds of cells. 

 The very numerous smaller cells are devoted to the functions of nutri- 







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-s' r5*T< 





-^f^ftfww 



Fig. 41. — Voh'ox, showing the small ciliated somatic cells and eight large germ-cells (drawn 

 from life by J. H. Emerion). 



tion and locomotion, and sooner or later die. Eic^ht or more larucr 

 cells are set aside as germ-cells, each of which by progressive fission 

 may form a new individual like the parent. In this case the germ- 

 cells are simply scattered about among the somatic cells, and no 

 special sexual organs exist. In all the higher types the germ-cells 

 are more or less definitely aggregated in groups, supported and 

 nourished by somatic cells specially set apart for that purpose and 

 forming distinct sexual organs, the ovaries and spcrmaries or their 

 equivalents. Within these organs the germ-cells are carried, pro- 

 tected, and nourished ; and here they undergo various differentia- 

 tions to prepare them for their future functions. 



