214 ESSENTIALS OF BIOLOGY 



is it, but organic developments are vastly more probable and so 

 they suggest processes that do not occur at random, but which 

 are tendential ones. 



Lastly, we again look at the chemistry of chromatin, the hypo- 

 thetical developmental substance. We note its relative simplicity ; 

 the entire want of any suggestion, or indication of its power of 

 self-differentiation. We note that all that chemistry suggests is 

 that nucleo-proteid appears to be a material very suitable for rapid 

 and versatile chemical transformations in conditions where these 

 transformations may be directed ones. We notice, also, that 

 there is no continuity of the chromatic materials in, say, the history 

 of the maturation of a gonidial cell, or in the phases of the nuclear 

 divisions that occur when the ovum segments. There are 

 " resting phases " in which the nucleo-protein of the chromosomes 

 is dispersed, hydrolyzed or otherwise chemically changes. It is 

 true that the chromosomes are reconstituted^ in their typical 

 numbers and forms, after the resting phases. It is said that even 

 when the chromosomes have lost their staining reactions — that 

 is, are no longer nucleo-protein^ *' ghosts " of their forms may still 

 be seen in the nucleus. But plainly this means that it is the 

 morphology of the nucleus, and not its chemistry that we are 

 studying. 



ii. It is organisrtial in nature. 

 That is, whatever activities we see in the living organism are 

 also in the developing embryo : the latter is mobile, irritable, 

 assimilatory, etc., and it even reproduces in that it undergoes 

 nuclear and cell-divisions. An algal zoospore or a polychaete 

 trochospere larva are clearly autonomous organisms that move 

 about and assimilate in sea-water. The embryo contained in a 

 yolked egg, or developing in a uterus assimilates and grows in 

 mass (although its most salient activity is the tectonic one and this 

 overshadows the other activities). The developmental phase that 

 we call a larval one is plainly a phase in which the thing that 

 develops by metamorphosis is, in all respects save reproduction, 

 an organism. We tend, somehow, to think of the developing 

 thing as not yet, but about to become an organism, but this view 

 is clearly inaccurate. 



Hi. It exhibits J in a predominant way, tectonic activities. 

 Although the thing that develops is truly an organism what is 

 significant in its organization is a tectonic activity. It selects 



