44 



LECTURE IV. 



The cavitary worms of Cuvier include the cylindrical species or 

 round worms which form the order Nematoidea of Rudolphi. 



This great entozoologist, who devoted the leisure of a long life 

 to the successful study of the present uninviting class, divided the 

 parenchymatous Entozoa into four other orders. The Acanthocephala, 

 in which the head has a retractile proboscis armed with recurved 

 spines, the body round and elongated, and the sexes in distinct indi- 

 viduals. The Trematoda, in which the head is unarmed and has a 

 suctorious foramen, the body rounded or flattened, and generally one 

 or more suctorious cavities for adhesion, and in which the organs of 

 both sexes are in the same individual. The Cestoidea, in which the 

 body is elongated, flattened, and generally articulated. The head, 

 variously organised, is generally provided with suctorious cavities and 

 a central mouth, sometimes armed with a coronet of hooks, some- 

 times with four unarmed or uncinated tentacles. Both kinds of genera- 

 tive organs are combined in the same individual. Lastly, the order 

 Cystica, in which the body is rounded or flattened, and terminates 

 posteriorly in a cyst, which is sometimes common to many indi- 

 viduals. The head is provided with suctorious cavities; and the 

 mouth, with a circle of hooklets, or with four unarmed or uncinated 

 tentacles. No distinct generative organs are developed in the cystic 

 Entozoa. 



The anatomy of the Entozoa is so distinct in each of these orders 

 that I shall describe it successively in a few typical species, selecting 

 more especially for demonstration those M'hich infest the human body ; 

 and which chiefly concern the medical practitioner. 



In this category the common pathological product, called ' Acepha- 

 locyst ' by Laennec, is by many received, and ought not, perhaps, in 

 this place to be omitted . The acephalocy st (Jig. 1 7> ^) consists of a sub- 

 globular or oval vesicle filled with 

 fluid. Sometimes suspended freely in 

 the fluid of a cyst of the surrounding 

 condensed cellular tissue (a) ; some- 

 times attached to such a cyst ; de- 

 veloping smaller acephalocysts, which 

 are discharged from the outer or the 

 inner surface of the parent cyst. 

 These acephalocysts vary from the 

 size of a pea to that of a child's head. In the larger ones the wall of 

 the cyst has a distinctly laminated texture. They are of a pearly 

 whiteness, without fibrous structure, elastic, spurting out their fluid 

 when punctured. Their tissue is composed chiefly of a substance 

 closely analogous to albumen, but differing by its solubility in hydro- 



Acephalocj'st. 



