94 



LECTURE VI. 



been already observed that they very closely resemble a composite 

 form of Trematnda. The extensive and natural group formed by 

 the two androgynous orders of " Sterelmintha " form, therefore, the 

 equivalent of the Nematoidea. The Acanthoeephala constitute a 

 more limited, yet natural order ; and the Linguatulce {Pentastoma of 

 Rudolphi) are the type of an analogous cii-cumscribed group ( Oncho- 

 phora) with a higher type of organisation, which entitles them to 

 rank in the class Codelmintha. This class includes all the cavitary 

 intestinal worms of Cuvier, with the exception of the " Vers ridi- 

 gules " of Lamarck, or Epizoa, which are proved by their metamor- 

 phoses 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 

 4Q principal internal parasites of the human sub- 



ject : viz. Trichina spiralis, Filaria medinensis, 

 Filaria oculi, Filaria bronchialis, Trichocephalus 

 dispar, Spiroptera hotninis, Strongylus gigas, 

 Ascaris lumbricoides, and Ascaris or Oxyurus 

 vermicularis. To the order Nematoidea, repeated 

 examinations, since my first observation of the 

 minute Trichina spiralis *, induce me to refer 

 that singular microscopic parasite (^^. 40.). I have 

 satisfied myself of the accuracy of Dr. Farre'sf 

 and Dr. Henle's J description of the distinct canal 

 in the cavity of the body. In a specimen of 

 Trichina now under the microscope, a loop of this 

 canal 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 first made known in an interesting case pub- 

 lished by Mr. Hilton § : and many others have since been recorded. 



The cysts are very readily detected by gently com- 

 pressing a thin slice of the infected muscle between two 

 pieces of glass and applying a magnifying power of an inch 

 focus. They are of an elliptical figure, with the extremi- 

 ties more or less attenuated, often unequally elongated, and 

 always more opake than the body or intermediate part of 

 the cyst, which is, in general, sufficiently transparent to 

 show that it contains a minute coiled-up worm (^g. 41.). 

 The usual size of the cyst is ^^jth of an inch in the long 

 *^itfc%t"*^ diameter, and -j-Jot^i^ o^ an inch across their middle part, 

 magii.' The cysts are arranged with their long axis parallel to 

 the course of the muscular fibres (^g. 40.), which probably results 

 * LXXX. vol.i. p. 315. t LXXX*. J LXXXI. p. 528. § LXXXH. 



Cysts of Trichina, in situ. 

 Nat. size. 



Trichina 



