PROFESSOR WEISMANN' S THEORIES. 475 



have quoted above, a crack in the doctrine is admitted : it is said 

 that "this differentiation was not at first absolute, and indeed it 

 is not always so to-day." And then, on turning to page 74, we 

 find that the crack has become a chasm. Of the reproductive 

 cells it is stated that — " In Vertebrata they do not become distinct 

 from the other cells of the body until the embryo is completely 

 formed." That is to say, in this large and most important division 

 of the animal kingdom, the implied universal law does not hold. 

 Much more than this is confessed. Lower down the page we read 

 — " There may be in fact cases in which such separation does not 

 take place until after the animal is completely formed, and others, 

 as I believe that I have shown, in which it first arises one or more 

 generations later, viz., in the buds produced by the parent." 



So that in other great divisions of the animal kingdom the 

 alleged law is broken ; as among the Codenterata by the Hydrozoa, 

 as among the MoTlusca by the Ascidians, and as among the An- 

 nuloida by the Trematode worms. 



Even in ordinary life, a man whose supposition proves to be 

 flatly contradicted by observation, is expected to hesitate ; though, 

 unhappily, he very often does not. But in the world of science, 

 one who finds his hypothesis at variance with large parts of the 

 evidence, forthwith abandons it. Not so Prof. Weismann. If he 

 does not say with the speculative Frenchman, " tant pis pour les 

 fails," he practically says something equivalent : — Propound your 

 hypothesis ; compare it with the facts ; and if the facts do not 

 agree with it, then assume potential fulfillment where you see no 

 actual fulfillment. For this is what he does. Following his ad- 

 mission above quoted, concerning the Vertebrata, come certain 

 sentences which I partially italicize : 



"Thus, as their development shows, a marked antithesis exists between the 

 substance of the undying reproductive cells and that of the perishable body-cells. 

 We can not explain this fact except oy the opposition that each reproductive cell 

 potentially contains two kinds of substance, which at a variable time after the 

 commencement of embryonic development, separate from one another, and finally 

 produce two sharply contrasted groups of cells " (p. 74). 



And a little lower down the page we meet with the lines : 



" It is therefore quite conceivable that the reproductive cells might separate 

 from the somatic cells mnch later than in the examples mentioned above, without 

 changing the hereditary tendencies of which they are the bearers." 



That is to say, it is " quite conceivable " that after sexless 

 CercaricB have gone on multiplying by internal gemmation for 

 generations, the two kinds of substance " have, notwithstanding 

 innumerable cell-divisions, preserved their respective natures, and 

 finally separate in such ways as to produce reproductive cells. 

 Here Prof. Weismann does not, as in a case before noted, assume 



