302 



BIOLOGICAL PHYSICS 



developmental sequence, a real nervous system, but entirely 

 of the sympathetic variety, in virtue of each cell of the 

 community, into which the primal cell, has divided, and 

 subdivided, being held together, and innervated, by a 

 process, or processes, uniting each unit, or cell, and 

 directing their individual work, for communal purposes. 

 In the limbed, and voluntarily moving, animal, a third 

 form of nervous system is evolved from the second, as 



FIG. 126. STAGES IN THE DIVISION OF THE OVUM OR EGG-CELL OF A 

 WORM. (Strasburger.) 



a, resting state ; b, nucleus transformed into a spindle-shaped system of fibres, which 

 are provided with thickenings at the equator of the spindle ; c, separation of 

 equatorial thickenings into two parts which gradually travel towards the poles of 

 the spindle and there become transformed into new (daughter) nuclei, whilst the 

 protoplasm at the same time also separates into two parts (d, e,f) ', g, repetition 

 of the division process, formation of spindles in daughter cells ; //, result of the 

 division of these. (The nuclear filaments are here probably only represented by 

 the thickenings at the equator of the spindle-shaped system, which is mainly 

 formed by fine straight filaments, which stain far less with haematoxylin than the 

 others, and on account probably of their less distinctness and want of colouration 

 are not seen. 



the second is from the first, by which its many multi- 

 cellular organs, and parts, are made to subserve the, 

 common purposes, and co-ordinated functional work, of 

 a complex organism this nervous system is called the 

 systemic nervous system, and is under voluntary control. 

 Arising out of, and evolved from, this systemic nervous 

 system, is a great central nerve organism, the brain (Fig. 

 127), which, in the human species, reaches such a 

 magnitude, and complexity of structure, and relationship 



