64 ENTOZOA. 



may frequently be found sexually united to the female in a 

 manner similar to that which obtains in Sclerostoma Syngamus. 

 In the male Sph^rularia, however, as in Gordius, there are no 

 special copulatory organs, or, to say the least, there are no 

 intromittent spicules. 



OxTURiD^. — The little thread-worms though by many asso- 

 ciated with the Ascarides proper, may be fitly and conveniently 

 arranged in a separate family by themselves. Their minute bulk, 

 fusiform shape, rounded oral aperture — which only resembles the 

 triangular mouth of Ascaris in the expanded or protruded con- 

 dition — their relative and strongly-marked disparity of size as 

 regards the sexes, the spurious character of the so-called alseform 

 appendages of the head, the triquetrous oesophagus and globular 

 form of the stomach, the highly developed nervous system, and, 

 more particularly, the single spiculum constituting the penis of the 

 male — these several peculiarities, all taken together, appear to me 

 sufficient to justify their separation from the true Ascarides. As I 

 have elsewhere remarked, the genera and species of Nematoda 

 display less tangible characters for systematic classification than 

 those exhibited by other classes of helminths. 



As a detailed account of the structure and development of the 

 common thread- worm {Oxyuris vermicularis) will be given in the 

 second division of this work, it will suffice my purpose to offer 

 at present only a very general description of the anatomy of 

 another member of this family. Our knowledge on this score is 

 chiefly due to the investigations of Walter, whose elaborate account 

 of the structure of Oxyuris ornata was first published in the eighth 

 volume of Siebold and KoUiker's Zeitsclirift, for 1857. The inte- 

 gument consists of an outer epidermis overlying a densely fibrous 

 corium or true skin, which latter is also made up, apparently, of 

 two layers. Externally, as in round worms generally, the body 

 is marked by numerous transverse stri^, but the latter are so 

 fine, even in the larger species, that they require considerable en- 

 largement in order to bring them into view. The muscular system 



