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FKEE NEMATOIDS. 
By H. CPIAELTON BASTIAN, M.D., F.L.S. 
T he word Nematoid ” is one, perhaps, not very familiar to 
general readers ; but no suitable popular equivalent can be 
substituted. When it is stated that one of the most numerously 
represented groups of the great assemblage of animals known 
as Entozoa has received this name, and that the animals of this 
particular Nematoid group have been usually known as round 
worms,” owing to their elongated, cylindrical, or more or less 
spindle-shaped form, readers to whom the name is unfamiliar 
will be approximating towards a comprehension of the nature of 
the animals, whose structure and life-history are to be the 
subject of this paper. But they will be approximating only, 
for the animals concerning which I am to treat are not Para- 
sitic, but Free Nematoids. 
The parasitic division of the Nematoid group includes such 
formidable and well-known human parasites as the now 
celebrated “Trichina,” the Dracunculus or Griiinea-worm, also 
an animal which produces the disease known as “Egyptian 
chlorosis,” and the common round worm, or Ascaris lumbri- 
coides — besides a host of others of more or less note, infesting 
animals of all kinds, even those as low in the scale as Medusse. 
And this constitutes one of the most interesting facts concern- 
ing the order Nematoidea, that it is made up in part of para- 
sites, and in part of representatives, even more numerous still, 
which are never parasites at any period of their life, but which 
lead a “ free ” existence in the most various external habitats. 
Our knowledge concerning these latter animals is almost 
entirely of recent date, only a very few representatives of this 
subdivision having been imperfectly known for a century and a 
half or two centuries. 
Notwithstanding the fact that they have been so much over- 
looked, in this country especially, the free Nematoids or 
Anguillulid^ constitute one of the most widely diffused 
groups of animals, the representatives of which are met with in 
the most various natural habitats. So remarkable are they in 
