DEVELOPMENT. 135 



"We may most conveniently consider it under the heads hence 

 arising. 



Total insubordination among the centres of develocinest, 

 is shown where the units or cells, as fast as they are severally 

 formed, part company and lead independent lives. This, in 

 the vegetal kingdom, habitually occurs among the Proto- 

 plnjta; and in the animal kingdom, among the Proto- 

 zoa. Partial insubordination is seen in those 

 somewhat advanced organisms, that consist of units which, 

 though they have not separated, have so little mutual depend- 

 ence that the aggregate they form is irregular. Among 

 plants, the Thallogens very generally exemplify this mode of 

 development. Lichens, spreading with flat or corrugated 

 edges in this or that direction, as the conditions determine, 

 have no manifest co-ordination of parts. In the Algce, the 

 Nostocs similarly show us an unsymmetrical structure. Of 

 Fungi, the sessile and creeping kinds display no further 

 dependence of one part on another, than is implied by their 

 cohesion. And even in such better-organized plants as the 

 Marchantia, the general arrangement shows no reference to a 

 directive centre. Among animals, many of the Sponges may 

 be cited as being thus devoid of that co-ordination implied 

 by symmetry : the Amaoba-like units composing them, though 

 they have some subordination to local centres, have no subor- 

 dination to a general centre. To distinguish that 

 kind of development in which the whole product of a germ 

 coheres in one mass, from that kind of development in which 

 it does not, Professor Huxley has introduced the words " con- 

 tinuous " and " discontinuous ;" and these seem the best fitted 

 for the purpose. Multicentral development, then, is divisible 

 into continuous and discontinuous. 



From central development we pass insensibly to that higher 

 kind of development for which axial seems the most appro- 

 priate name. A tendency towards this is vaguely manifested 

 almost everywhere. The great majority even of Protophyta 

 and Protozoa have different longitudinal and transverse di- 



