4: THE DISEASES OF DOMESTIC ANIMALS. 



cially in the males ; head narrow, finely pointed, unarmed, with a 

 simple, central, minute oval aperture ; posterior extremity of the 

 male furnished with a bilobed caudal appendage, the cloacal or 

 anal aperture being situated between these divergent appendages ; 

 penis consisting of a single spicule, cleft above, so as to assume a 

 V-shaped outline ; female stouter than the male, bluntly rounded 

 posteriorly, with genital outlet placed forward at about the end of the 

 first fifth of the long diameter of the body. Eggs measuring y^w 

 of an inch from pole to pole ; mode of reproduction viviparous." 



" The shell-less ova develop into minute embryos immediately on 

 fructification, and completely fill the uterus of the female, and are 

 born in immense numbers." * " The embryos measure, previous to 

 birth, about ten micrometres in length, and five to six in transverse 

 diameter. The study of the structure of the embryo is almost im- 

 possible so long as it is retained within the body of the maternal 

 parasite. Here it resembles a delicate thread, having a somewhat 

 uniform granular appearance, which becomes less distinct as devel- 

 opment progresses. In the older embryos — extra-maternal — we 

 may perceive a very delicate cuticle and an axial line running 

 through the body ; the extremities are more or less blunt, and not 

 easily to be distinguished as to which is the posterior or anterior 

 end of the parasite. In the intestines the embryos measure about 

 0*1 mm. in length, sometimes more, and have a transverse diameter 

 of about 6 /i." (Pagenstecker.) 



" Within the abdominal cavity they may be found to measure 

 from 0*12 to 0*16 mm. in length, with a transverse diameter of 8 fju. 

 They have scarcely ever been seen less than 0"12 mm. in length 

 when in the muscles. Comparison with mature trichinae indicates 

 that the slenderer of the two extremities is the head." 



" The posterior extremity possesses more rigidity than the ante- 

 rior, and also seems to have a backward and forward motion. The 

 rigid condition of the terminal end of the parasitic embryo corre- 

 sponds with the situation, or limits, of the axial line, which is looked 

 upon as the rudimentary alimentary canal. The anterior portion of 

 the embryo is not granulous, but clear, being only modified by a 

 delicate chitin thread which is continuous with the cuticle, and con- 

 stitutes the first indication of the chitinous lining of the oval cavity. 

 As development progresses, this axial line divides into two parts ; 

 the anterior portion corresponds to the so-called cell-body of the 

 mature parasite, and the posterior to the stomach, intestines, etc. 

 The sexual organs can not, as yet, be distinguished. The embryos 

 * Leuckart, "Die menschlichen Parasiten," vol. ii, p. 512. 



