PHYSIOLOGICAL (OR CONSTITUTIONAL) UNITS. 613 



as it does the proclivity of the constitutional units towards the 

 structure of the species, allies itself with the phenomena of both 

 agamogenesis and gamogenesis. The first of these shows us how 

 a fissiparously-detached portion of the parental tissue takes on 

 the same form as the parent; and the second shows how those 

 small detached portions distinguished as sperm-cell and germ-cell 

 also, when united and supplied with the needful materials, do the 

 same thing. 



4. But the set of phenomena following the union of sperm-cell 

 and germ-cell differ in a certain way from those which follow 

 when a gemma or other unfertilized portion of parental tissue is 

 detached. The incomprehensibleness of this difference as other- 

 wise contemplated, and the partial comprehensibleness of it when 

 joined with the hypothesis of physiological units, furnish a 

 further support for the hypothesis. 



The familiar truth learnt by the tyro in algebra that an ap- 

 parent solution which contains the unknown quantity is no 

 solution, is a truth apt to be overlooked in other spheres than 

 the algebraic. An illustration is supplied by the answer once 

 given in Parliament to the question " What is an Archdeacon ? " 

 " One who discharges archidiaconal functions." But science as 

 well as daily life furnishes examples. When it is said by Engel- 

 mann, Hensen, Hertwig, and Maupas that " the essential end of 

 sexuality is rejuvenescence, that is, the restoration of growth- 

 energy," we have another instance of an explanation which explains 

 nothing. W T hat is the phenomenon to be explained ? That un- 

 folding of an organism from a germ which displays growth-energy. 

 And what is the explanation ? The giving of fresh growth-energy. 

 The unknown quantity " growth-energy " is contained in the 

 explanation proposed. There exists no conception of "juven- 

 escence " save that derived from observing developing plants and 

 animals ; and if " re " be prefixed, no interpretation is thereby 

 given to the unexplained thing " juvenescence." 



Coleridge somewhere comments on a source of fallacy which he 

 calls the " hypostasis of a relation " the changing of a relation 

 into a thing. The plumber who tells you that water rises in a 

 pump " by suction " supplies an instance. Having assumed suction 

 to be an agent, he thinks that he understands how the piston does 

 its work. Some of the explanations given of fertilization supply 

 further instances. When it is said that sexual union has for its 

 end " to give increased vigour to all the vital processes," it is 

 tacitly implied that vigour is a something a something which 

 can be given. But now, in the first place, it is only by the hypo- 

 stasis of a relation that we are led to think of vigour as a thing. 

 Vigour is a state that state of a living body which enables it to 



