THK DEVELOPMENT OK TIIK NEMATOIDEA. .VJ9 



The female reproductive apparatus is, at first, represented 

 !>v ;i solid cellular body which lies in the mesoderm ; though 

 whether it 01 i LI inally belongs to this, or to the ectoderm, or 

 to the endoderm, is not clear. The cellular body acquires a 

 tubular form, and eventually opens externally by uniting 

 with ;in inward process of the ectoderm, which gives rise to 

 the van-inn. 



The young cast their cuticle twice first, when they leave 

 the egg, and, again, when they acquire their sexual organ.-. 



The Nematoidea have been divided into three principal 

 groups * Polymyaria, Meromyaria, and Holomyaria char- 

 acterized by the nature of their muscular system. 



In the Poly my aria, the muscles of the parietes of the 

 body are divided into many series, each made up of many 

 " muscle-cells." In the Meromyaria there are only eight 

 longitudinal series of such muscle-cells, two between each 

 lateral area and the dorsal and ventral lines respectively. In 

 the Holomyuria the muscles are not divided into* series of 

 muscle-cells. 



The first two divisions contain only such genera as an- 

 swer to the general description just given ; but, in the Jfolo- 

 myaria, there are included several aberrant forms. Thus, 

 Trichocephalus has no lateral areas; Ichthyonema has no 

 anus ; Mermis has no anus, and the alimentary canal is rudi- 

 mentary, though it possesses the lateral areas, and the males 

 have spicula. Gordius has no lateral areas, and only the 

 ventral line ; the alimentary canal is reduced to a rudiment, 

 without either oral or anal aperture, and the male has no 

 spicula. In both these genera the anterior ends of the em- 

 bryos are provided with spines, which aid them to bore their 

 way into the bodies of the insects on which they are para- 

 sitic. In Sphcerufaria the alimentary canal is similarly rudi- 

 mentary, and Sir John Lubbock discovered that the small 

 male becomes permanently adherent to the female. 



Some Nematoidea (e. g., Leptodera, Pelodera) live in 

 water or damp earth, and are never actually parasitic; but 

 they require abundant nitrogenous food in order to develop 

 their sexual organs, and hence they are found in the sexual 



1 Schneider, " Monographic der Nematoden," 1866. flee also Bastian, 

 "Monograph of the Anguillulida? " (" Trans. Linnfean Society," 186M; and, 

 " On the Anatomy and Physioloffy of the Nematoids " (" Phil.' Trans.," 1866) ; 

 and several memoirs by BfttBOhu. The latter affirms that the muscles are as 

 much made up of muscle-cells in the Holmnyari't, as in the rest. ("Giebt 68 

 Holomyarier I " Zeitschriftfur wiss. Zoologu, 1873.) 



