_ ON MYORYKTES WEISMANNI. 29 
The female generative tube is double, and the vaginal ori- 
fice slightly prominent, or placed at the commencement of the 
hinder fourth of the length. 
The ¢estis is a short, cylindrical tube, which opens with 
the intestine. There is a pair of spicula. 
The rudimentary generative products consisted of minute 
nuclei. In the female these were surrounded with a gra- 
nular substance, and became minute polygonal egg-cells. In 
the male no further development towards zoosperms was ob- 
served. Nothing definite as regards nerves and ganglia 
could be made out. 
In the first case, the author, besides the thoracic muscle, 
found some of the parasites in various other striped muscles, 
as in the tongue and heart, although in small numbers; they 
were also seen by him in the peritoneal coat of the liver, 
and in the submucous tissue on the tongue. None were 
found, though sought for, in the intestine and other viscera, 
nor under the peritoneum of the abdominal cavity. The 
young condition of the parasites, the frequent occurrence of 
free individuals in the conncctive tissue, left no room for 
doubt that they had only just commenced their migration. 
The author endeavoured, therefore, by further observations, 
to ascertain the ultimate fate of the host. 
In all, ninety individuals of Rana temporaria were examined 
—thirteen with success. In spring (March), the author found 
the parasite always in every sixth frog, to the number of two 
or three in the thoracic muscle; whilst in June, in thirty- 
one frogs, they occurred only three times in three distinct 
individuals, and never more than one in each. At this time, 
therefore, they had become rarer, especially the males, which 
were never met with after April. 
The investigation was carried on in the remainder of the 
winter-frogs, in some of which the parasites had been first 
noticed. Of fresh frogs, the author has examined only a 
few, and these without success. They are not included 
amongst the ninety above mentioned. 
Afterwards the author confined his examination to the 
thoracic muscle, being convinced that the minute and deli- 
cate parasites may be easily overlooked in preparations which 
are not very transparent ; nor in the other muscles is it easy 
to make equally thin sections without disturbing the fibres. 
Even in the thoracic muscle it is often difficult to perceive 
the nematodes. 
It next became evident that the parasites, having once 
penetrated into the tissues, increased in size as the season 
advanced, and arrived at sexual maturity. Whilst in March 
