ORIGIN OF INTESTINAL WORMS. 23 



of intestinal worms could be readily explained. They were a 

 striking instance of spontaneous generation, the existence of which 

 was already contended for in by far the greater number of the 

 lower animals. At most, the discussion related to the particular 

 formative material out of which the newly created organism was 

 made, and whether it was first an egg or appeared at once as 

 an adult. Sometimes it was the blood and juices of the body, at 

 another time the excretions of the alimentary canal or the digested 

 food, that was supposed to be the formative substratum of the 

 spontaneous generation ; and it was disputed as to whether fermenta- 

 tion or putrefaction, or a special organizing principle, gave the first 

 impulse to its creation. 



These were the opinions held by the Ancients, and throughout the 

 Middle Ages, so fruitless in scientific research. It was not until the 

 seventeenth century that the theory of the generation of animals was 

 reformed, and at the same time an entire revolution in the opinions as 

 to the origin of Entozoa inaugurated. 



The researches of Swammerdam and Eedi had the most profound 

 influence, and entirely contradicted the earlier theories, that sexual 

 generation was confined to the higher animals. They showed that 

 sexual generation, precisely similar to that of birds, mammals, &c., 

 was found in many of the lower animals ; such as the insect, whose 

 development and metamorphosis were for the first time worked out by 

 these two naturalists ; not even the parasitic insects being neglected. 



Eedi clearly proved by his researches and experiments that the 

 maggots, which had been formerly considered as independent organ- 

 isms (Helcophagi), were in reality the larvse of flies, and that they were 

 only developed when the fully formed insects were allowed access to 

 deposit their eggs. 1 Swammerdam, in the same way, showed that lice 

 were developed from eggs ; 2 he was also well aware (according to the 

 communications of the painter 0. Marsilius) that the parasitic larvse 

 in caterpillars were the offspring of insects that were in the habit of 

 laying their eggs beneath the skin of these same caterpillars. 3 



With respect to the intestinal worms, neither of these observers 

 brought any direct evidence against the generally received opinions. 

 Certainly not Eedi, who put forward a view as to their origin, 

 which differed only by a somewhat metaphysical tinge from the 

 widely spread theory of generatio cequivoca. Swammerdam expressly 

 guards against any application of his experiments concerning the 

 development of insects to the Entozoa. It appears, indeed, as if he 



1 Redi, " Esperienze intorno agl' insetti," t. i. p. 23 : Venezia, 1712. 



2 "Bibel der Natur" (aus dem Hollandischen Ubersetzt), p. 37, 1752. 

 8 Ibid., p. 28L 



