62 LECTURE VI. 



chiefly occupy our attention in the present lecture. The Cystica, 

 Cestoidea, Trematoda, and Acanthoceplicda are far from being 

 respectively equivalent to the order Nematoidea, either as regards 

 grade, difference, or circumscription of organic characters. Tlie 

 transition from the cystic to the tsenioid Entozoa is so gradual and 

 close, by the Cysticercus fasciolaris, for example, that they are com- 

 bined in the same order " Tcenioidea," in the " Regne Animal " of 

 Cuvier. On the other hand, Cuvier separates the jointless LigulcB in 

 which the head has neither suckers, bothria, nor uncinated proboscis, 

 from the Tsenioids, and limits the order Cestoidea to the Ligulce. 

 It is hardly possible, however, to separate from the Taenioids of 

 Cuvier, the intestinal Z?<7?//g; of birds, in which traces of both bothria 

 and generative organs begin to manifest themselves. With respect 

 to the higher organised Cestoidea of Iludolphi, it has been already 

 observed that they are essentially a composite form of Trematoda. 

 The extensive and natural group formed by the three androgynous 

 orders of " Sterelmintha" form, therefore, the equivalent of the 

 Nematoidea. The Acanthocephala constitute a more limited, yet 

 natural order; and i\\e Lingua tulce {Pentastoma of Rudolphi) are 

 the type of an analogous circumscribed group with a higher type of 

 organisation, which entitles them to rank in the class Ciclelmintha. 

 This class includes all the cavitary intestinal worms of Cuvier, with 

 the exception of the "Vers ridigules" or Epizoa, which are proved 

 by their metamorphoses to belong to the siphonostomous Crustaceans. 

 The order Nematoidea, which forms the chief part of the class 

 Codelmintha, must chiefly interest the physician, since it includes the 

 principal internal parasites of the human subject : viz. Trichina 

 spiralis, Filaria medinensis, Filaria ocidi, Filaria hroncJiialis, Tri- 

 chocephalns dispar, Spiroptera hominis, Strongylus gigas, Ascaris 

 bimbricoides, and Ascaris or Oxyurus vermicidaris. To the order 

 Nematoidea, repeated examinations, since my first observation of the 

 minute Trichina spiralis*, induce me to refer that singular micro- 

 scopic parasite. I have satisfied myself of the accuracy of Dr. Farre's 

 and Dr. Henle's description of the distinct alimentary canal. In a 

 specimen of Trichina now under the microscope, a loop of the 

 intestine may be seen protruding through a rupture of the abdominal 

 wall. The vermicule is always contained in a cyst. The occurrence 

 of these cysts in vast numbers in the muscular tissue was made 

 known in a very interesting case published by Mr. Hilton f : and 

 many others have since been recorded. 



* Transactions of the Zoological Society, vol. i. p. 315. 

 t Medical Gazette, February, 1833. 



