282 THE SCHOOL OF R:eAUMUR 



Trembley's worst mistake was that he supposed the 

 base of the polyp to be perforated. When we recollect 

 that he worked with a simple lens, and lacked all the 

 appliances which histological experience has now devised, 

 it is surprising that he should have ascertained that the 

 body- wall is composed of two layers, the colouring 

 matter being confined to the inner one ; that both 

 layers extend into the hollow tentacles ; and that the 

 cavity of a bud is continuous with the cavity of the 

 parent polyp. 



Trembley carefully abstains from the guessing which 

 so often spoils the work of early discoverers. " Je ne 

 m'arreterai point," he says, "a expliquer par quel 

 m^canisme le corps des polypes s'etend et se contracte. 

 Je risquerais de ne donner que des conjectures." He 

 would no doubt have gone wrong if he had oiFered an 

 explanation. 



His manipulative skill is astonishing. There are very 

 few who could lay open a Hydra in this way : " Je mets 

 un polype sur ma main, et je le fais contracter le plus 

 qu'il est possible ; aprfes quoi j'introduis dans sa bouche 

 une pointe de ciseaux tres fins, et je la fais sortir par le 

 bout post^rieur. Je ferme ensuite les ciseaux, c'est-a- 

 dire, je coupe un cotd de la peau du polype suivant 

 toute sa longueur, j'ouvre d'un bout a I'autre le canal 

 qu'elle forme, et en abaissant aprfes cela de c6t^ et 

 d'autre cette peau que j'ai s6par6e, je d^couvre la super- 

 ficie int^rieure de la peau du polype, les parois de son 

 estomac." Trembley cut Hydras into very minute 

 pieces, which completed themselves into normal polyps ; 

 he divided them longitudinally as well as transversely, 

 and actually succeeded in cutting a polyp into four 

 strips, each of which yielded a perfect animal. By 

 cutting and reuniting he produced extraordinary mon- 



