336 PARASITES OF ANIMALS 



made known more particularly by Leuckart. But the facts 

 thus conveyed do not explain the whole truth ; or, rather, they 

 convey it only in a very incomplete manner. Professor Leuckart's 

 experiments were made with several species such as Strongylus 

 armatus of the horse, S. rufescens, 8. hypostomus, and S.filaria 

 of the sheep, and 8. commutatus of the hare. Still, as regards 

 the strongyles, partial as the results have thus far appeared, 

 there cannot be a doubt that his successes with several allied 

 nematode species form a key by which we may yet unlock and 

 expose to view the entire life-history of that specially obnoxious 

 form under consideration, namely, Strongylus micrurus. To 

 summarise the whole matter in a few words, Leuckart supposes 

 that all these strongyloids require a change of hosts before they 

 can take up their final abode in the sexually-mature state. This 

 he infers especially because their respective embryos display 

 characters very similar to those exhibited by Olulanus. He 

 believes that either small mollusks or insects and their larvae 

 play the role of intermediary bearer. His experiments with the 

 embryos of Strongylus filaria prove that these larvae can be kept 

 alive for several weeks in moist earth, and that whilst so 

 conditioned they undergo a first change of skin within a period 

 varying from eight to fourteen days. Experiments on sheep, 

 made with these moulting larvae, led only to negative results. 

 Unless the following facts be accepted, the scientific position 

 remains pretty much where Leuckart left it. 



On the 22nd of October, 1875, at 1 p.m., I placed the entire 

 egg-contents of the- uterus of a Strongylus micrurus on a glass 

 slide hollowed out in the centre. Probably something like ten 

 thousand ova were thus brought under observation, yet only 

 three were noticed as freed from their shells, probably as the 

 result of accidental rupture. Two of these displayed lively 

 movements. In round numbers the ova gave a measurement 

 of ago of an inch in length by ^ of an inch in breadth, whilst 

 the free embryos measured about ^ of an inch long, and less 

 than o of an inch in thickness. The integument of the embryo 

 displayed neither markings of any kind nor any double contour. 

 The contents of the worm were gnanular throughout, these 

 granules being crowded in the centre of the body, but scarcely 

 visible towards the head and tail, where for a considerable 

 space (fully T^") the worm was perfectly transparent. No trace 

 of any sexual organs or their outlets was visible. An examina- 

 tion of numerous eggs and free embryos obtained from near the 



