Parasites: A Treatise on the Entozoa of Man and Animals: Including Some Account of the EctozoaCobbold, T. Spencer (Thomas Spencer)
Science
Parasites: A Treatise on the Entozoa of Man and Animals: Including Some Account of the Ectozoa
Cobbold, T. Spencer (Thomas Spencer)
Helminths; Parasites
I estimated their greatest
length and breadth to be 1/30″ by 1/1000″. Robin and myself thought
we recognised a distinct, rounded, anal orifice; and whilst Busk, on
the one hand, saw nothing which in the slightest degree indicated the
presence of an anal opening, Carter, on the other hand, described the
structure which we called the anus as a gland, at the same time placing
the alimentary outlet on one side and a little above it. According to
Bastian, “the intestinal tube is about 1/87″ in length, and appears
to consist of a simple canal of varying calibre, pursuing a nearly
straight course, and terminating exactly at about the middle, in length,
of the worm.” Like Robin, Bastian recognised œsophageal and stomachal
divisions, and in a few examples he observed the cæcal or terminal
portion of the intestine to be partially reflected upon itself. In
regard to the circular opening which Robin and myself described as the
anus, Bastian says there is a rounded body, “about 1/2200″ in diameter,
with a dark or light spot in the centre, according to the varying focal
distance, and which seems to represent a central aperture. Sometimes,
above this, traces of two or three large cells may be recognised, whilst
behind nothing definite can be made out, save that the cavity of the
body is visible for about 1/400″. In other specimens of the young worm
the central body and spot are wanting, but, in its stead, two lateral
sacculi are met with, about 1/3300″ in diameter, that communicate
with the exterior by a minute channel through the integuments, which
can sometimes be distinctly recognised. At other times the channel is
obscured by protrusion, which appears to have taken place through it,
of a minute bilobed papilla, projecting 1/10,000″ from the side of the
body. When the projections are seen, the sacculi are indistinct.”
[Illustration: FIG. 44.--Embryos of _Dracunculus_. Magnified 500
diameters. After Bastian.]
As Bastian found the young in all stages of development from the
germ condition 1/5000″ in diameter up to the perfect embryo, and as,
moreover, he, like the rest of us, could detect no sexual orifice in
the adult Dracunculus, he was led to express his belief that the young
were produced agamogenetically. He went so far as to call the germs
_pseudova_. It was with great reluctance that I dissented from the views
of so gifted an observer as Bastian; nevertheless, later researches have
shown that I was justified in not hastily concurring in the theory of a
non-sexual mode of reproduction for Dracunculus.
Public-domain text, read in full here on John Shaqi.
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