IV 



VEIIMES—SYSTEMA TIC RE VIE W 



179 



muddy earth. Sexes separate. The females are viviparous, and produce only a few 

 young (1 at most), which, after being hatched, find their way into the lungs of 

 frogs and toads, and there 

 develop into mature her- 

 maphrodite animals {Asmris 

 iiigrovenosa), from whose fer- 

 tilised eggs the free - living 

 Ehaiditis generation again 

 arises. The life-history thus 

 exhibits a sort of heterogeny, 

 Sphcerularia homhi, the Rhah- 

 diiis-like young form lives 

 in the earth. The fertilised 



females find their way into 



the female humble bee, where 



they are parasitic in the body 



cavity or in the intestine. 



The uterus, which is filled 



with embryos, soon begins to 



hang out from the female 



genital aperture, and becomes 



a large pouch, to which 



the worm-body finally forms 



merely a small insignificant 



appendage. MerTnithidce,viit\\- 



out anus. The young are 



parasitic in the body cavity 



of Insects ; they make their 



way out into damp earth, 



where they become sexually 



mature and reproduce them- 

 selves ; Mermis nigrescens. 

 Filariidm : Filaria medin- 



ensis (medina worm), may 



have a breadth of 0'5-2 mm. 



and length of nearly a metre ; 



in the subcutaneous connec- 

 tive tissue of man, in warm 



regions of the Old World. 



The young in small Crustacea 



(Cyclopidce). Trichotrachelidw: 



Trichocephalus dispar, with 



swollen hinder body, in the 



human caecum. 



Trichina spiiralis (Fig. 



121) lives sexually mature 



as the so-called intestinal 



Trichina in the small intestine 



of man and in that of many 



mammals ; is viviparous ; the 



female (B) is ca. 3 mm., the male (CO half as long. 



Fig. 121.— Triohma spiralis (after Claus). A, Encysted 

 muscle Triohlna ; m/, unaltered muscle fibres ; /, fat globules ; 

 cy, cyst ; Vh, envelope of connective tissue. J3, Female Intes- 

 tinal Trichina ; ob, ovary ; e, embryos ; zt, cell bodies (in the 

 post CESophageal division of the intestine) ; wo, female aperture. 

 C, Male intestinal Trichina ; a, ossophagus ; %, testis ; ie, 

 ductus ejaculatorius. 



_ The young bore their way 



inkTtheTntestinal wall, pass from here through the body cavity, or with the blood 



