STERKLMINTHA. 83 



mules, which grow from the membranous walls of the sac ; and 

 which, having attained a certain growth, become detached, and are 

 found floating in the glairy fluid contained in the interior of the 

 parent. 



(113.) It is difficult even to conjecture the manner in which 

 these parasites first obtain admission to the localities where they are 

 found, and some zoologists have been content to allow the possi- 

 bility of their being spontaneously generated : but the present 

 state of our knowledge can scarcely sanction the occurrence of 

 such developements. It seems more probable to imagine that 

 the entozoa exist in some other form under other circumstances, 

 but that, when introduced into the body, their eggs may be 

 conveyed by the circulating fluids to a nidus proper for their 

 developement, where their inordinate growth is due to the 

 abundant supply of already animalized food placed within their 

 reach, and the exalted temperature at which they are kept. 



(114.) The Trichina spiralis (fig. 35) is an entozoon hitherto 

 only found in the human body, Fig. 35. 



and, although of recent dis- ii; ;i|lliuilla -M^^ 

 co very, several cases of its oc- | 

 currence are recorded. This 

 minute worm is found in im- 

 mense numbers imbedded in 

 the cellular intervals between 

 the muscular fibres, and in 

 some instances all the vo- 

 luntary muscles seem full of 

 these creatures, exhibiting, 

 when viewed with the naked 

 eye, an appearance imitated 

 in the annexed figure (fig. 35, c.) * On examining the white 

 specks attentively under the microscope, every one of them is 

 seen to be a flask-shaped vesicle, apparently formed of condensed 

 cellular membrane, in which the minute animal is lodged ; and 

 when this outer covering is ruptured, as at (a), the worm escapes. 

 A magnified view of the entozoon is given at (6), coiled up in the 

 position in which it is seen prior to the destruction of the sac 

 which enclosed it. The body seems to be filled with granular 



* For the knowledge which we possess of the anatomy of Trichina, we are princi- 

 pally indebted to the researches of Professor Owen and Dr. Arthur Farre ; though 



it was first discovered by M. Hilton, Vide Zool. Trans, vol. i. 



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