116 LECTURE VI. 



Entozoa taken into account. A nematoid worm 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 codfish 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 oviparous 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 Strongylus ijiflexus 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 embryo assumes 

 the form of an echinococcus, the head being provided with six hooks. 

 So armed it is enabled to attach itself to the species of animal in which 

 it becomes encysted and undergoes its next transformation : and such 

 species, being the food of the higher organised animal in which the 

 ultimate metamorphosis of the taenia takes place, the pupal tape-worm 

 is in that way introduced into its final abode. So far as observations 

 have yet gone, two different animals, having the mutual relation of 

 prey and devourer, are subordinated, so to speak, to the well-being of 

 each species of tape- worm. The metamorphoses of the Trematoda are 

 still more astonishing, and the locomotive condition of the earlier phases 

 of the Distoma evidently relate to the securing their entry into the 

 animal's body, which they are destined either temporarily in a larval 

 state, or permanently, to infest. Siebold has noticed the difference 

 of form between the j^oung 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 suppose its multitu- 

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



