PARASITES FKEE WHILE YOUNG. 155 



among the Leptoderse. This is another instance of a 

 parasite on a parasite. 



While speaking of these worms, I will allude to a 

 nematode which I observed under very singular circum- 

 stances. I had a considerable number of skeletons or, I 

 should rather say, separate bones, exposed to the sun 

 upon a roof to whiten ; among these skeletons there 

 were several hyperoodons and other cetacea. All these 

 bones had remained for a certain time in horse-dung in 

 order to hasten the decomposition of the soft parts. They 

 had been in the open air for several weeks, and were 

 slowly bleaching ; it had rained nearly every day. 

 Towards the end of the month of August, I examined 

 some of the vertebrae, and found them quite black on the 

 upper part. Below, I discovered a mass of syrupy 

 matter, slightly yellow, like pus that has recently issued 

 from a wound. The sun was shining full upon the 

 bones at this time ; looking at them more closely, I saw 

 this pus issuing from the holes which convey nourish- 

 ment to the substance of the vertebrae ; it seemed that 

 the inside of the bones was in full fermentation. Ex- 

 amining it with some attention, I perceived that the 

 whole surface was in motion ; an undulatory wriggling 

 covered it as if a ciliated skin had been stretched above 

 the orifices. I took a little of this matter on the point 

 of a scalpel, and observed it with the microscope, and 

 what was my astonishment when I saw the whole mass 

 in motion . as if under the influence of a magic wand. 

 "When I slightly compressed it afterwards between two 

 slips of glass, there remained nothing before my eyes 

 but nematode worms of very small size wriggling over 

 each other : I found males by the side of their females ; 



