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XXII. The Re/;roductirm of the Ascaris mystax. By Henry Nelson, M.D. 
Communicated hy Allen Thomson, M.D., F.R.S., Professor of Anatomy in the 
University of Glasgow. 
Received May 22, — Read June 5, 1851. 
Having been led to investigate the mode of generation and development of the 
Ascaris mystax, I venture to lay before the Royal Society the results of my observa- 
tions, in the hope that they may not be devoid of interest. 
The worm in question has been long known to helminthologists (Plate XXV*. 
figs. 3 and 4); it varies from 1 to 3 inches in length, is fusiform, and covered with a 
striated horny cuticle, which is projected on either side of the head to form the alee 
charaeteristic of the species (fig. 1 a). 
The Ascaris mystax is found within the intestinal canal of the domestic Cat. So 
common is it, that out of about thirty examined for the purpose I have not failed to 
find them in more than three or four cases. 
The part in which they are generally found in the greatest abundance is that por- 
tion of the duodenum between the pylorus and the opening of the bile-duct. When 
the cat has fasted for some hours, the Ascarides pass the pyloric valve into the sto- 
mach, apparently in search of food; but this is never the case during digestion; on 
the contrary, they appear to be then svi^ept further down the intestinal canal than 
the part they normally occupy. 
The male Ascaris mystax (fig. 3) is about an inch and a quarter in length ; while 
the female (fig. 4) is from 2 to 3 inches, and occasionally even 4 inches. 
The males are easily distinguishable by their size and the peculiar curve of their 
tails (fig. 3 a), which are coiled round on the ventral aspect, while those of the 
females increase slightly in thickness to within a short distance of their termination, 
and are perfectly straight without any curvature of the point (fig. 4 a). 
This creature derives its specific name from two lateral projections on either side 
of the head resembling moustaches (fig. 1 a). These projections or alge are flat, 
transparent and striated, being covered by the horny cuticle which envelopes the 
whole body (fig. 1 d). In front is the mouth with its three lobes (fig. 1 h) opening 
directly into the intestinal canal (fig. 1 c). The entire body is covered with cartilagi- 
nous rings placed side by side and exactly of the same breadth, tlie whole forming 
one continuous cuticular envelope, appearing to be regularly striated when viewed 
externally (fig. \ d). 
4 D 
MDCCCLII. 
