80 LECTURE YI. 



beyond the powers of endurance of the Rotifera, and which would be 

 truly surpi'ising were not the simplicity of the organisation of the 

 Entozoa taken into account. A Nematoid woi'ni has been seen to 

 exhibit strong contortions — evident vital motions — after having been 

 subjected above an hour to the temperature of boiling water, with a 

 cod-fish which it infested ; and, on the other hand, Rudolphi relates 

 that the Entozoa of the genus Capsularia, which infest the herrings 

 that are annually sent to Berlin, hard frozen and packed in ice, do, 

 when thawed, manifest unequivocal signs of restored vitality. If, 

 then, the fully developed and mature Entozoa can resist such 

 powerful extraneous causes of destruction, how much more must the 

 ova possess the power of enduring such without losing their latent 

 life. 



Burdach, who has summed up the evidence at great length in 

 favour of the equivocal generation of the Entozoa, adduces the 

 example of the ovoviparous species as involving the limitation of the 

 offspring to the lifetime of the individual which they themselves 

 infest ; but on this point Dr. Eschricht * has well observed that the 

 transmission of the living young of the Strongyhis iiiJJexus from one 

 porpoise to another is readily explicable. This species of Strongylus 

 lives in the bronchial tubes, with its head immersed in the substance 

 of the lungs, and its tail extended into the larger branches of the 

 trachea. The living young must naturally escape into the mouth, 

 and, as porpoises are gregarious, the young worms would, by a short 

 passage through the water, readily be introduced into the mouth of 

 another porpoise, and so reach the trachea. 



The young of most Entozoa are subject to metamorphoses. I 

 have already alluded to those of the Cestoidea in which the head 

 in all the species seems first to be provided with six hooks. -|- 

 Those of the Trematoda are the most astonishing, and the loco- 

 motive condition of the young Dlstomata evidently relate to the 

 securing their entry into the animal's body which they are destined 

 to infest. Dr. Siebold has noticed the difference of form between 

 the young of the Echinorhynchi and their viviparous parents ; and 

 this difference was so great in regard to the viviparous Filaria 

 medinensis, that Dr. Jacobson was led to supjwse its multitudinous 

 progeny to be parasites of the parasite. Dr. Eschricht has observed 

 that the flesh of fishes in summer is often studded with small worms, 

 which, in one instance, he ascertained to be Echinorhynclii ; and he 

 su"-gests whether it may not be the breeding place of such species, 



* Essay on Spontaneous Generation, Edinb. Philos. Journal, vol. xxxi. p. 345. 

 f Dujardin, in Annales de Science Nat. 1838. 



