80 LECTURE V. 



LECTURE V. 



ENTOZOA. 



The essential anatomical character of the third order of Entozoa in 

 the classification of Rudolphi may be represented by combining the 

 head of an unarmed Taenia, with one of its joints, containing the fully 

 developed androgynous organs. The digestive system being repre- 

 sented by simple canals, imbedded in the soft cellular parenchyme, 

 and without anal outlet. 



The Trematoda may be characterised as having a soft, flattened, 

 rarely rounded, body, with an indistinct head, an unarmed mouth, 

 and generally one or more suckers for adhesion in different parts of 

 the body : the organs of both sexes are in the same individual. 



Rudolphi was a pupil and ardent admirer of Linnaeus, and adopted 

 external and easily recognisable characters for the generic sub- 

 divisions of the Trematode order, the species of which he distributed 

 according to the number and positions of the suctorious orifices and 

 cavities. When there is a single one, it constitutes the genus Mono- 

 stoma : when there are two, which are terminal or at opposite ends of 

 the body, you have the character of the genus Amphistoma : when 

 the posterior of the two suckers is not terminal, but on the inferior 

 surface of the body, this constitutes the genus Distoma : three suc- 

 torious cavities characterise the genus Tristoma ; five, the genus 

 Pentastoma ; and a greater number that called Polystoma. Subse- 

 quent anatomical investigations have led to the formation of other 

 genera of Trematoda, and have likewise shown that those 'species 

 which were grouped together by the external and artificial characters 

 of the Rudolphian system, manifest differences of organisation, 

 indicating, at least, the generic distinction of such species : nay, 

 most of the Pentastomata of Rudolphi appertain to the Coelelminthic 

 class of Entozoa. 



My illustrations of the anatomy of this order will 

 be chiefly derived from the two species which infest 

 the human subject ; these are the Distoma hepaticum 

 {fig. 36.), and the Distoma lanceolatum {fig. 37.). 

 Both are peculiar to the biliary ducts and gall bladder, 

 but may pass thence into the intestine. Both, like- 

 wise, are more commonly found in the ordinary 

 domestic animals, as the sheep and ox, than in the 

 Din. hepaticum, human subject. 



A full-grown Distoma hepaticum is of a flattened, 

 ovate, or oblong-ovate form, broader and rounded anteriorly, attenu- 



