NEMATOIDEA. 39 



with horn-like plates, or with actual hooks ; the 

 oesophagus, or the stomach, is also often dilated and 

 muscular, or provided with horny plates, similar to 

 those situated at the mouth ; the remamder of the 

 intestine is generally straight, and presents no 

 special peculiarity. 



The ova of the nematoid worms are round or 

 elliptical, and sometimes burst whilst within the body 

 of the mother, according to Dujardin. 



The full-grown embryo possesses only the diges- 

 tive tube, and the general envelop of the body ; its 

 mouth is not furnished with a complex apparatus, 

 like that of the adult worm, and it has no repro- 

 ductive organs. 



It presents the general form of the adult, and 

 attains to its complete development without under- 

 going any metamorphosis. 



The female usually acquires much larger dimen- 

 sions than the male, and it is also more frequently 

 met with than the latter. 



The Nematoidea form a very large number of 

 species which, for the most part, hve parasitically 

 either in the hollow viscera, or in the tissues, of both 

 vertebrate and invertebrate animals. The mode of 

 transmission and of propagation of the nematoidea is 

 only known in a small proportion of species. In 

 some, the embryos are developed within the organ in 

 which the parent worms are contained, and in which 

 the latter had deposited their ova ; in others, they 

 are developed externally, and must, in order to attain 

 to the perfect state, pass into their natural abode 

 either in the condition of an embryo enclosed within 

 the ovum, or else of a free larva. In the latter case, 



